Here are some specification I think appropriate for you
1. choose a Laptop, not desktop
2. a core2duo laptop with 2GB RAM is more than enough
3. at least 1TB Hard disc
5. Medium quality brand such as DELL, TOSHIBA, HP, you do not need high quality brand such as APPLE, VAIO,
6. Screen size should not be smaller than 16"
7. It is assumed that you are not a student of multimedia, multimedia software require high performance pc, that I am not referring for you.
..........Happy college life