I can understand the choice of a Mac as it's great for graphic and video work but spending that amount of money I can't quite fathom.
We've got a few Macs in the family and they've proven to be quite expensive to run. Mainly because software isn't as widely available for the Mac as it is the PC. There's far more shareware and free software for the PC. We've noticed there seems to be a lot more "budget" software that is released as shareware than free.
When my mum bought her Mac she paid a bit extra to get a year worth of technical help from Apple themselves. That has now expired and she either has to pay more to get more support time or search through the net or ask me for help.
I've recently upgraded my PC to a high level for about £500. I've got dual core AMD, 1GB of DDR2 800 RAM (very fast), SATA hard drives and a nice 256MB GDDR3 graphics card.
I recently helped a friend build a new PC to a very silly spec level (includes dual core Intel, 768MB graphics card, 2GB DDR2 800, water cooled and 660MB SATA hard drives) In total he spent about £900. If applications/games get too intensive he can buy another 768MB graphics card and run the two side by side together.
My mum regularly gets an Apple Mac magazine (I think iCreate) and they mention the 8core Mac which uses two quad core Xeon processors. Benchmarks showed it didn't perform that much faster than two dual core processors.
The great thing with a PC is you can take anything out and upgrade it (other hardware permitting) where with a Mac it's not that simple. My brother has a (now quite old) tower based Mac and he's had thoughts of moving to a PC because it can be expanded so easily.
Two main sites I buy components from are
www.aria.co.uk and
www.komplett.co.uk.
You'll be surprised how cheap you can upgrade for or even build new.