Sampling record, using trim, then into a sequence

I am not sure how to go about this. I just recently purchased an MPC2000XL (finally!!!) and all I really can hook it up to are my turntables, so I am really just going thru old records looking for samples. I found this rawass bassline and I took just over 2 bars of the sample. How do I then turn that into a sequence? I dont have a beatcounter so the metronome isnt hitting at the right time as the sample, it's a lil off. Even after trying to fine tune the bpm. Also, when I put the sample into trim to trim the end, how can I tell what spike on the wavelength is what sound without hearing the sample as the wavelentgh registers? If the sample was a barebone beat, it would be easy to tell, but it isnt. I dont have an interface for my computer so I cant use a wave editor. I have to do it all on the MPC.

uppin,... help!

trim it to 2 bars then loop it and the mpc will tell you the tempo

go into trim and cut it down to 2 bars. Then goto edit then Timestrech. At the bottom one of the F-Keys say BPM. Set it for 8 beats (2 Bars) then it will tell you the source tempos bpm.