External DVD Burners and HDD's will be a pain in the tail end.
You will undoubtedly be at school working on your final project at the 11th hour and realize that the one file you need to complete your work is 3hrs away at home in your external HDD that is under your couch and no way to get to it in time. I advise to have enough HDD space on your laptop or PC to hold all required data. Backup to external HDD would be a good idea. Also, HDD to hold non-critical data would make sense, but you don't control when non-critical becomes critical.
External DVD burner is a pain in the *** as well. Do you remember me lugging around that external CD burner all over the country on P22T03? Freaking thing was as big and heavy as my Toughbook.
If you need a laptop, get one with enough HDD space and required media writer (CDRW, DVDRW, etc.)
If not, get a fat machine at home with all the HDD space and meida writers you can fit into the drive bays.
I think storage capacity is probably key. You probably don't need to be doing tons of MFLOPS of processing on your rearch papers. PIII with 200GB HDD and 512MB RAM may due for your school work.
The mission-criticle DegIcank tasks, on the other hand, may required a few more tasty MFLOPS.
The way we do it here at MiTech, is have a phat *** laptop to bring to our clients, and another phat *** system in the office to store, play and burn our EconoCanks.