I reckon you're always better off building machines yourself Aerbabe.
Not only will you save money but you get exactly what you want. Building your own really isn't difficult and is very satisfying. You could find a supplier offering exactly what you want but generally, almost universally, they include some rubbish in the system.
Personally I'd recommend Asus motherboards (especially the A8 series with integrated NVidia graphics and Audio), getting a reasonable case and a very good monitor. Go for a lowish end chip in the motherboard as the price of chips sinks through the floor faster than they can change the prices. Any chip in a newbuild system is seriously quick and you can upgrade once the mobos highest chip is dirt cheap. Same with memory really, 512 is always going to be more than enough and just bung a new chip or two in if you need more when its really dirt cheap.
Don't like the TFTs meself though useful if you are likely to move around a lot. You can get a seriously high end CRT which would have been several hundred quid and only used by DTP or CAD users for the cost of naff TFT now.
Figure on about £400 including monitor if you build one yourself. Don't buy the software, just enroll on a CPD course (£100) at your local uni and you can download any Microsoft software you want for free. XP and Office would set you back a lot more on their own....