Own build server (1 Viewer)

Hi
I built my last server and am wanting to upgrade but puzzling over spec. I wondered if someone could help. The server runs MS Small Business Server 2003 with ISA 2004 and has two purposes - first to power my own office network and second to keep myself fully familiar with SBS since I support a couple of client's servers.
My current setup is a 3.2GHz P4 processor on a decent level motherboard but not a server board. It is running on 1Gb non-ECC RAM. The OS is on 2 mirrored 80Gb SATA drives and the data is on 2 mirrored 300Gb SATA drives.
It all works pretty well but I do have an Active Directory issue I need to resolve.
I want to have another server at the ready in case I fluff the AD issue.

My plan was to utilise the case of my original HP server but replacing the old motherboard which was IDE not SATA, and replacing the old IDE discs with SATA discs. I may also have to replace the power supply and cooling but that is not a huge issue. The processor(s) and RAM are, however.
I am puzzling over 1) which would work better, a fast dual core Pentium Extreme processor or a Xeon processor (but with perhaps the capability to go to dual Xeon processors) and 2) do I go for a server board or just a high end normal motherboard.
As I see it I would probably need a serverboard anyway if I went for dual Xeon but if Pentium Extreme then I could get away with a normal board and then be able to use the cheaper non-ECC RAM rather than the ECC RAM a serverboard usually demands. So would dual Xeon really be worth the extra cost - I have no idea and also no idea how to find out, other than asking!

If anyone could shed some insight into how I might best make choices then it would be really helpful. Funds are a bit limited, so I cannot go wild, but I do recognise it would be an investment.
Thanks in anticipation

Is your server going to be used as an application server or is its main purpose for storage of information (eg documents etc?)

Hi
Thanks for the response
It will be the latter, storage of data and dishing it out to client PCs on demand.
I generally run my applications at the PC end within the network

In that case it wont need a lot of processing power. Your run of the mill P4 with a 800 FSB will do the job just fine and a fairly good quality motherboard the only other thing i would recommend is a good quality netwok card (you can neva have enough memory ut about 1 gig of ddr400 should do the job)

In that case it wont need a lot of processing power. Your run of the mill P4 with a 800 FSB will do the job just fine and a fairly good quality motherboard the only other thing i would recommend is a good quality netwok card (you can neva have enough memory but about 1 gig of ddr400 should do the job)

Thanks for that.
I will move ahead and see about building to more like my previous specifications but will use perhaps a better quality motherboard next time.
Best wishes