Cindy, I wouldn't recommend the ISIS. I have it and I'm saving up to ditch it for something better. There are several alternatives that allow you to plug in line level instruments like guitars and keys.
My reasons for dissing the ISIS: it records at 16 bits. The sound quality is not bad, but most every other card/interface combo out there now records at at least 20 bits, and believe me, you can hear the difference. When I first got the ISIS, it wouldn't work with my motherboard because of the VIA chipset. Guillemot exchanged it for one that would, but when I upgraded and got a Pentium rig, I had to do it again. Other quirks include not working with overclocked processors very well, driver issues, buggy bundled software.
Once you get a taste for computer recording, you're going to wish for better sound and more capability. There are good affordable packages out there. I'm saying you can do better without spending a lot more. Good luck, and let us know what you get and how it works!
-Kent