Suggestions please.....

Hi AllHaving established that upgrading my Dell Dimension 9200 to get better FSX performance is a non-starter (can't be overclocked, low-power PSU not enabling good video like 8800 etc.), I'm now looking at building a new computer....I'm on a budget, but want to use my existing DDR2 memory (2 MEG), hard-drives and DVD/CD writer. I guess I'm looking for a powerful PSU, case, mobo to have integrated Internet Broadband and sound capabilities, fast CPU (duo or quad?) and 'matching' chip set and fast/powerful graphics card.Also, what operating system would you recommend?This machine will primarilly run FSX, so please help with component suggestions with FSX performance as the main consideration.Right now, I have no idea where to start.....!Thanks for any help.Toni.