A comparable Dell would be the Inspiron 1525. It’s 600 dollars on the Dell website, compared to 500 on Amazon for the Compaq. It has a bit more RAM (3GB) and a bigger hard drive. However, it has a worse graphics card which may cause problems when running Vista.
There is a similar Acer laptop for 550 dollars, but it also has an inferior graphics card.
The Compaq’s hard drive is also pretty big, so that shouldn’t be a factor. Also, the 2 GB DDR2 memory on the Compaq should be adequate for running Vista. If you want more, you can always buy extra memory and install it yourself. An extra 2 GB of memory would only cost about 20 dollars.
I would probably go with the Compaq in this case.