which computer would you sugest out of the following

Hi my cousin needs a cheap desktop computer to run a database (local database not networked or anything). He would also like to go online every now and then, but its going to be used at a business mostly for his database program.

He currently has dos (ms dos 5.11) so ANYTHING will be an upgrade compared to that.

The database software has minimum requirements of 1gb of memory and XP (or WIN 7).

He does not want to spend more then $150 on a computer because the database program that he is updating to is very expensive (arround $900)

Below are a few computers that I was looking at:

http://www.staples.com/HP-DC5750-0027-Refurbished-Desktop-PC/product_913498

http://www.staples.com/HP-DC500-Rfurbished-Desktop-PC/product_499107

http://www.staples.com/HP-DC7100-0019-Refurbished-Desktop-PC/product_897052

http://www.staples.com/IBM-ThinkCentre-8215-0028-Refurbished-Desktop-PC/product_368532

Any sugestions?