budget question.

The Gen 5 is more upgradeable, but if you are on a budget, the 9100 is fine (and it is upgradeable, but has 1 or 2 fewer drive bays than the Gen 5 has).

Also, see these sites for some coupon deals to save some more money:
http://www.xpbargains.com/dell_coupons/
http://dell.coupons-coupon-codes.com/
http://www.fatwallet.com/deals.php
http://gotapex.com/