well what you could do is buy a 7200RPM drive right now, so and upgrade later when you have the cash for a 10K rpm moster..
but if at all possible, try to get a 10k rpm.
a 7200rpm SCSI drive is still better then 7200RPM IDE drives, becuase it's still oriented for low access time, and it also has the low CPU usage advantage. however throughput isn't as fast, becuase it's probably using a lower density disk (7200RPM SCSI drives are normally older then current IDE drives).