ftp://ftp.software.ibm.com/pc/pcinstitu ... tabook.pdf
If you open that pdf and do a search in acrobat reader for 2529-rcu you will go right to the appropriate page.
You can see it lists your model as the 100gb drive. Then if you look down in the row underneath that contains the SATA drive info, you see which models have which drives and at which speed. Your model has the 7200rpm.
That page is just for the models that are similar to yours, of course. But every model is in that tabook if you want to look at them all.
I bought the 2531-MTU, which came with the 100gb 5400rpm. The 7200rpm drives are a little quicker/snappier with no (or very little) increase in noise or vibration - they do use more battery, of course (but not too much).
EDIT: hmmm ... I guess I had this page open for a while - I didn't realize someone already responded.
