I have Paintshop Pro X4 Ultimate on my desktop, Photoshop CS3 on my laptop.
It depends on what sort of editing you are wanting to do. If you just want to enhance your pictures, do some fun effects to them, etc. Then you can probably get by with Paintshop Pro, which has the added bonus of coming with a number of filters from Nik software (only in the X4 Ultimate, and the recently released X5). Which can do all sorts of interesting stuff to your photos.
Photoshop can do all that (though without the filters, it can be tricky getting the same look, though there are a lot of free photoshop actions that can help). It can also do a bit more when it comes to editing/creating images that aren't photos.
Photoshop is also far more expensive. Since they just came out with an upgrade to Paintshop pro, the previous version (X4 Ultimate) should be cheaper. On Amazon they have X4 Ultimate for $47, the new version X5 Ultimate is almost $100 (for just a few new things and some improvements).
http://www.amazon.com/Corel-PaintShop-Pro-Ultimate-Version/dp/B005HTIWIQ/ref=sr_1_2?s=software&ie=UTF8&qid=1348118746&sr=1-2&keywords=Corel+PaintShop+Pro+X4 Link if you are curious.