If it a really old machine, the ide config may not support the boot for that larger DMA HD, that is if it is Ultra DMA 66 or higher, that old compac willnot read that new hard drive. You might need to buy an external USB HD enclosure and pull the data to your laptop that way. You can buy one on Newegg for not too much and then you'll have the enclosure for use with you laptop for addtional storage and back up (which you need anyway).
Noli Nothis Permittere Te Terere!!
EVGA 680i, Dual EVGA 8800GT'S (650/950), 4 gigs OCZ DDR2 1066, Intel Q9450 at 3.8 Ghz, Koolance Water Cooled, Dual Plextor16x DL DVD+/-RW. Dual WD 250gb 16mb Cache Sata 3.0. 3DMark06 score = 19,168.