I divided 20G to C and D partitions. WindowsXP and all my programs take about 5G in C drive. I did ghost backup for the whole C drive, and stored in D, which take another 2.4G. But I feel very comfortable now because I can easily restore the whole system in 10 minutes. (I do not use any kind of antivirus softwares because those softwares usually will slow down your machine a lot. But I do update the XP very often and opened the windows firewall. Anyway, I have been using XP since it released 3 years ago, so far, I have not got any virus problem. :D ) Mp3s take another 1-1.5G. My files for my work have used another 2G so far. Finally I still have 8-9G left. So, I think 20G is enough for me, at least at this stage. I do have another 40G external HD (3.5 inch, USB2.0) if I like I can store the movies and music video in that disk.