heh..... if you want good advice, read my post.... and read it good.
first off, dont buy anything from compusa, prices are deceiving their, the rebates take FOREVER, and if your product broke, ur not getting it replaced. TRUST me. they suck when it comes to customer service. their tech support is good, but thats one of their bigger money makers, that and being one of the only companies that fully support mac's. if you want a good drive from a good companie, go here:
www.newegg.com , their based out of california, they ship to usa only. ive been ordering things from them since 1997, back when they were called
www.egghead.com . great companie. ive built about 10-15 computers all parts from newegg, not one hard drive died out of any of those computers. another tip is to stay away from crappy companies, like maxtor/ibm (yes ibm hd's SUCK) and samsung. buy western digital, or seagate. its worth the extra $5-$10.
Externals are going to cost a crapload more then internals just cause their mobile and a breeze to install. if i were you, i would install the extra hard drive as a slave and just leave your c drive alone. if space is an issue on your current hard drive, move all your mp3s/videos/ non-installed applications to your extra hard drive. i currently have 4 hard drives in my pc, 3 western digitrals, and one seagat, total of about 220 gigis. ive had the 3 western digitals for 3 years, not one of them have given me problems. another recommendation i can make is, learn to partition your drive. doing that saves a lot of heartache. if your going to take out your current hard drive and start fresh with this new one, partition it so that you have primary and extended. primary for windows, extended for data storage. that way you can always format the c parition if it came down to that, cause windows isnt perfect. compusa isnt bad if its a " i NEED something RIGHT now " situation. but if you want to save money and get great service, buy from newegg.com , if you order anything, you usually get it in 2 days from fedex. and all warranty's apply to their products just like things would if you bought it from compusa or best buy. and if you do indeed want a retail box/software with your hard drive, dont buy the OEM, OEM only gives you the hard drive, nothing else. save money dude, research the options, make sure you dont erase your important shiz. externals are crap btw. just my .02, look at my avatar and smile, cause you know you want to.