Sal the cabbie was baffled.

"You wanna go where?" he asked in his cab parked in front of the Parker House in downtown Boston.

"Hopkinton," I said. "You know, where they start the Boston marathon."

"Hey, pal, they ran that race yesterday. Didn't you see the paper?

"I know," I said. "But I'm going to run it today."

Forty-five minutes and 26 1/2 miles later, Sal the cabbie knew I was serious. "Hey, pal, do me a favor," he said before letting me out of at the foot of Hayden Rowe Street smack in the middle of Hopkinton. "Go slow."

No worry, Sal I always do.

I had started running less than 10 months ago, mostly to spend my progress on the most serious diet of my life. Plainly put, I discovered the more I ran, the more I could eat and still lose weight.

At first, a half-mile jog was sheer huff-and-huff agony. But as the pounds were going poof, my breath was coming back. Now, 90 pounds lighter, my regimen includes six to eight miles a day, at a 10-minute-a-mile pace.

That was far too slow to qualify for Boston, but nothing could stop me - save for common sense - from running the course the following day. And so, at 8:37 a.m., coated from shoulder to feet with Vaseline to prevent chafing, I was off on a one-man marathon.

It was so easy at the start, mostly downhill, even if the wind was blowing in my face. The previous day, the entire route had been closed the traffic and leaders in the race had motorcycled police escorts as they wooshed into Boston at five minutes-a-mile.

Tuesday, it was every man - actually just this man - for himself in the face of two lanes of traffic, cracked sidewalks, rocky-road shoulders and, worst of all, trailer trucks, kicking up dust and pebbles. And every other truck just had to blow his horn.

At the three-mile mark, just outside Ashland, a snapping dog came charging from its snooze on a front porch, gave chase for a half a block then stopped suddenly, praise be, when I wheeled and cussed back.

The first break came at seven miles, in Framingham. It took all of 60 seconds to dash into the Seven-11, plunk down 35 cents (I carried $20 in cash, a room-key, more Vaseline and an American Express card in an old sock) for 12 ounces of lukewarm iced tea. It was a pause that truly refreshed.

At 10 miles, I was churning comfortably through Natick, admiring the lovely old homes, the manicured lawns and hardly even noticing that I had been on the road for 100 minutes, the longest run of my life.

This can't last, my head kept saying. Four miles later, my legs got the message. Now, every step seemed a struggle, pains were shooting out from my lower back and my mouth felt as if I had just licked 600 envelopes.

It was time to stop - first to buy a new pair of socks (mine were soaked), then a quart of orange juice in the Star Market in Wellesley Hills. Twenty minutes later, the grind continued.

The hills began at the 16-mile mark, just after I had crossed the Charles River. I was walking now, past Newton-Wellesley Hospital, resisted the urge to collapse in the emergency room, and continued on past the Newton Fire Station, where the second of the four toughest hills began.

At this point the previous day, Bill Rodgers, the marathon champion, made his move to take the lead. On Tuesday I made a bold move, too. I started running again, past the Brae Burn Country Club and all the way to a small cluster of stores at the foot of the last major obstacle the torture test known as Heartbreak Hill.

Clearly, it was time for decisive action. I stopped at one of those shops that specialized in wine and cheese and had a beer. And a morsel of Muenster. It didn't help, so I began walking up Heartbreak, tipsy.

About 100 yards up, a little boy on a bicycle came whooshing past me going downhill. "Faster," he yelled. Slightly embarrassed, I began running again, ever so slowly, all the way to the top, panting furiously as I crept past Boston College and caught my first glimpse of the Prudential Center six miles away.

For the previous four miles, I had been seriously entertaining thoughts of hitchhiking back in, maybe even hailing a cab. But now, with the end literally in sight, I knew nothing less than a heart attack would stop me.

I walked-ran the next three miles, took a wrong left turn off the course for about 400 yards before I realized I was heading in the wrong direction, then stopped again in sacred territory - the Bill Rodgers Running Center at Cleveland Circle, three miles from the finish.

I'm not even sure why I went inside. Perhaps a whiff of air, or a glimpse of the champion waiting on a customer would give me new life. But Rodgers wasn't there; Colman McCarthy, a colleague from the paper who had run the marathon in 3:28 the previous day, was. He was shopping for shirts.

"You running the course," he asked. I nodded yes.Barely.

"How long you been out," he asked.

"Since 8:30," I said. McCarthy looked at the wall clock, saw it was now 1 p.m., held back a snicker and offered encouragement.

"Only three miles to go, you've got it made," he said. "Just keep drinking fluids."

And so, I was off for the homestretch, down Beacon Street, through my first crowd of the day at Kenmore Square (they were all heading for Fenway Park and a Red Sox game) back to Commonwealth Avinue, right on Hereford Street, left at the Prudential Buuilding and a sweet 100-yard downhill to the yellow finish line.

"Twenty-four hours too late," a wise guy yelled from across the street, but I paid no attention. I had completed the course at 2:13 p.m., five hours and 36 minutes after I started. Of the 26 miles, 385 yards, I believe I ran about 22 miles, more than twice as far as these weary legs had ever carried me before.

It is over now. My right foot is tender to the touch, and I can hardly bend my right knee, but the sweet memory of finishing the Boston Marathon course, standing up will last at least until next fall.

They're running a marathon through the streets of Washington on Nov. 5. I might try again on the proper day.