Advice on Desktop PC configuration - to boost Excel performance

Hi,
Not strictly an Excel question.. but..

I'm using Office2007 Pro with Windows XP.
Desktop PC is dual core Pentiunm 4 HT with 3 GB ram

The excel files I manipulate can get quite large (pushing 100mb) and calculation time is extremely long.
The spreadsheet I'm working on now takes more than half an hour to calculate.

I'm trying to get my corporate IT department to get me a PC with faster processing power and would like feedback on the kind of configuration other heavy XL users have found works well for them.
Ram doesn't seem to be a problem - not sure of access times though - the processor(s) just chug along at 100% most of the time.


Any and all advice welcome.

Thanks

Thanks!
I'll digest this while waiting for XL to do it's thing.

Quick glance through show I've not done anything glaringly inefficient.

Cheers