Hmm , never noticed any performance difference between XP on SATA and XP on PATA

... yes ... 5400 rpm hdd with lower read buffers will mean slightly more access time , but not something drastic .. finally , it depends on how well ur XP is optimized for its performance ..
If u really want more performance out of the SATA hdd than over ur PATA , just keep the page file on the SATA drive , no matter where u install XP ..
The performance boost when using SATA drives is noticeable only when u run two or more drives in RAID ..