When buying a PC designed for manipulating photographs there are some features that you should look out for.
First and foremost, a good monitor is essential. The basic idea is that the screen should be capable of showing exactly how the photo will look when it is printed. If you are reading this on a TFT screen, try this simple test. Look at your display from different angles and you will probably notice that the brightness varies. A screen is said to have good viewing angles if the picture remains consistent with different viewing angles. This is one of the most basic requirements, and so most good quality TFTs should have consistent results.
The colour accuracy and contrast ratios are also really important measures of how well a screen performs. It starts to get quite technical and at this point - so you will need to rely on a professional's word for it. A lot of people make the mistake of listening to the claims of the manufacturer or salesman. They will often bend the truth to make their own product seem most favourable. I almost never listen to manufacturer's claims - even the technical specs can be misleading.
It is far better to read reviews in magazines - these are normally unbiased, but you should make sure they have reviewed the product in depth. I like to use the online version of PCmag.com and PCpro.co.uk. The products they have given awards to always live up to their reputation.
The PC itself should have a spec that is suited to the size of photos that you are using. If you have a 10 megapixel camera for professional shooting, a large hard drive will be necessary. Photo libraries typically require each photo to be 50-200MB in size. If you are looking to backup all of your photos on a drive you can see that even a 200GB drive may well only be large enough to store 1000-2000.
If you are working with photos over 6-7 mega pixels, I would recommend you having 1 GB of RAM. For 10-12 megapixel photos perhaps you will need 1.5-2 GBs depending on how on how adventurous you want to get with Photoshop.
The CPU's power won't make much difference to just browsing your snaps. However, if you want to make full use of Photoshop's filters, then a faster CPU will mean less waiting around.