Seoul,
Time compression can work if it's minimal. It basically inserts tiny bits of space into the sample so that it still has the same frequencies and pitch, just slowed down a little. Sometimes it can work, if it's not far off from the tempo, other times it really sounds choppy because it's drastic. I've used this as an effect once or twice to a vocal, stretching it out 3 or 4 times the length, making it sound like the Matrix, u know... when the Neo touches the mirror.
But if you need to time compress just a hair, to make sure it matches up to exactly the right tempo, here's what I've done:
Use the "tap tempo" and find the tempo that's closest to the sample. Say you come up with 87.1 bpm. It's probably 87 exactly, and you tapped slighly off. Try a drum line to 87 and match it up. If it's off by a little, then it might mean that whoever performed the original didn't have a click track to perform to, and it's off by a little. This is usually the case when sampling symphonic or orchestral shit. You can use time compression a little bit, just to round off to the nearest bpm, and it won't sound bad at all. If it's 87 bpm, and you think it needs to be a little faster or slower, I wouldn't stretch it out more than 5 bpm. Anything more than that might sound fake.
If you don't have the tap function...
I've selected one beat (one 1/4 note) of the sample and found the miliseconds, then divided 60 over this number to get the tempo. (60 / 0.625 = 96 bpm) If it's close to the tempo, it's probably accurate. (You might get 0.623 or something and get 96.3 bpm) This just helps to find the tempo when you need it.
You can also chop up the sample so that you have it broken down in 1/4 or 1/8 notes, and just place them where you want em. This is a good function to either spread across your mpc or use in FL so that you can stutter the actual notes of the sample and really get a sick hip hop feel.
Most of this shit you probably already know. But sometimes it helps when other people spell it out.
Hope this helped,
Hypno