Go for the Dell stuff, it would be hard to get things cheaper. They are masters of upselling though - I went on their site a few months ago to buy a new PC, mainly used for surfing and some development work. The PC that would suit my needs suddenly became the ultimate behemoth of PCs because I wanted all the latest sexy stuff...
However, what I really wanted to comment on was that big systems do make programmers lazy. Gertrude and others being the exception. Its because the machines are so powerful and fast with GB of RAM that even a 'slow' application runs at an acceptable pace. Now that might sound acceptable, but last year I had to diagnose some bad code... Developers bear with me - it was in
VB.NET, with MS Access, with code using pass thru T-SQL to a SQL Server. A right dogs dinner of code and loops and jumps. I almost cried in desparation then got to work on fixing literally dozens of lines of codes in three languages in three apps into a SINGLE line of code embedded in MS Access (with some funky relationships added to the DB table). The point here is that if the 'professional' developers don't have a clue what they are doing - because it all runs fast enough - they are storing up huge trouble in future for maintenance, modifications, bug fixing etc. - Which is why I was asked to look in the first place - the system had broken down. If the developers had to write stuff on a slower box they would have immediately realised their code was too cumbersome and done something about it (i.e. read the manuals!) and learned to be a bit more efficient.