The keys are processor speed, memory, and disk space. If you can afford it, get about the 2nd fastest processor available (fastest available is always a big jump in price). For the XPS it looks like 3.0Ghz, which is plenty fast. Next is RAM, and a good start is 1GB. The XPS has a fast frontside bus, which is important, and upgrading to 1GB of RAM will help speed things up. Finally disk space, 80GB is minimum and since you apparently have a lot of tapes you should upgrade to at least 120GB. I have 2 120GB drives and the extra space comes in handy. Consider adding a 2nd drive with serial ATA interface (you can always do it later though).
Another option worth considering is a DVD burner. Prices for both the burner and blank media have come way down and it's nice to be able to edit videos and then burn them to DVD to give to friends. They are also good for making backups of your hard drives.