I would have to say that the HDD does appear to be of use no more
Couple of tips for purchasing a new desktop, make sure that it has 8GB of Ram and at least a 2GHz dual or quad core processor, preferably quad as it will give you headroom for more demanding future software, for Photoshop an add on video card would be best but nothing too fancy, a DVD drive for installing and burning disks and finally avoid SFF (small form factor) computers as they are notoriously difficult to upgrade, use none standard size and shape power supplies + they tend to run hot because of the limited space inside the case trapping the hot air.
If you see any computers that interest you post a link and we will gladly take a look at the specs for you.