First BONZO2000, you need to ask yourself "what am I going to be using it for". Once you have decided that you are half way there.
A few pointers:
1) is it for gaming?
if so then go for a high spec machine, top graphics card, processor and plenty of Ram (DDR)
2) is just to surf the internet and use the Office programs to a small degree?
if so then middle of the range PC's should do.
3) if it is just to surf the net then the lower range of PC's will do.
Remeber all PC's can be upgraded at a later date.
As for recommendations for a supplier, I would suggest you read some of the posts in here and Computer magazines to decide.