They are very similar

(A) Dell Precision D/T 340 P4 - 2ghz, 80gb, 512mb, DVD-RW

(B) Dell GX270 Desktop P4 2.8GHz 512MB 80GB DVD+RW & XP Pro

The second one is better because (1) the processor has a faster clock speed (2.8 GHz instead of 2 GHz). But both processors are Pentium 4. Also (2) the second computer seems to come with XP Pro (and the first computer does not say. You may have to pay extra for the operating system for the first computer.) Both have the same amount of memory (512 MB). I would suggest that you get 1 GB of memory if you will be using Windows XP (1 GB of memory is twice as much as 512 MB of memory. And adding memory should not be too expensive. Ask. I would guess about $40 ???)

If you can afford it - - consider getting a better processor (instead of a Pentium 4). I would suggest staying with a Pentium - - but see if you can afford a "dual processor". That means that there are two processors. If you get a dual processor with at least 1.4 GHz of clock speed - - that would be as much clock speed as the Pentium 4 with 2.8 GHz