My PC works perfectly well using with 2-year (or is it 3-year?) old components - a Gigabyte GA-MA78G-DS3H. Graphics is a ATI Radeon HD 3200 built into the motherbaord, CPU is a AMD Phenom X4 9750, it has 4GB RAM, runs W7x64. I use CS4, I admit it takes time to do a panorama from several images from my K7 but suspect most PCs would... Screen is an Eizo.
I plan getting a second IPS screen at some point in time, a bottom-end one. I used to have two screens, I put the image on one and all the various palettes, toolbars and so on on the other.
If you can find an affordable IPS screen that will rotate 90 degrees that can be very useful if you are editing large Word documents. I found it invaluable for finishing my degree project, when I had reached the final stage of re-reading and making sure it was beautifully laid out - I could see each page full-size.
Backups are essential. I have an NAS (I got it to put my CDs onto) with two disks in a mirror, I use SyncToy to backup to it, and I also have quite a lot of stuff backed up to an extra HDD in the PC. I also have an external HDD.... Synctoy comes from Microsoft and is an excellent little utility.
Mentioning my degree reminds me - if you can find a way to qualify for student software it can save a bundle. I did a cheap Open University course a while back and the cost the course, plus W7, plus Office 2010 (the Pro version), plus CS4, was less than a retail copy of CS4. I keep debating doing another course and getting Lightroom except I'd have to put quite a lot of effort into understanding it. All that export business and so on... I might have to buy 'Lightroom for Dummies'!