Singlespeed & Fixed Gear - suspension forks

i have a mountain bike that i'm going to convert to a singlespeed. i know nothing about mountain bikes. it has one of those suspension forks, whose purpose i understand if you are actually riding the bike on a mountain. what about the street though? i think it's significantly heavier than a standard mtb forks, but what i'm really not sure of is if it will make the bike a lot slower...i feel like the answer is yes, but i really don't know. it just seems like the shock absorption would slow it down...

The short answer is yes, it will slow you down. Older shocks were especially bad. Every time you push down on the pedal, the shock would compress a bit, which takes energy away from driving the bike. If its a fairly new, higher end, fork, the problem won't be as noticable, but it will still be there. If you're only going to ride on the road, get a solid fork and some skinny tires. Or just look for a decent, older road bike.

i have a nice fixed gear road bike. we've got a giant boulder mtb from a few years ago that just hangs out since my girlfriend switched to a road bike. i dumpster a lot, but refuse to put a rack + milk crate on my bike, so i'm gonna make the giant a utility bike. plus then i can ride over curbs. and babies.

Might as well leave it on if it is in some sort of working order... Beaters are fine any way they are, and you might like the added comfort. You can always drop it later. BTW I myself hate suspension forks with a vengeance... Added weight, thief magnet, and it stabs you in the back when you try to accelerate out of the saddle. I almost threw up when I tried to sprint on a FS MTB with knobbies on asphalt. Rocking up and down, making a helluva racket and basically staying on the same spot was what happened.

If you've got access to a cheap rigid fork, do it. Otherwise, unless you REALLY hate the old sus fork, just stiffen the crap out of it (if it has any adjustment at all) and ride it.