Right, so I think it's done for now anyway.....

- Wiped HDD and removed the old Win NT intall
- Installed XP Pro
- Found all drivers, everything working
- Modified and installed MX440 s-video card, configured PC to use s-video as primary monitor and fiddled with settings till half decent
- Tested PC's resources/stableness by playing music and video simultainiously from USB HDD into PC - ran stable

So all I really need to do now is;

- buy and fit PCI optical audio card (to pass through DTS and DD5.1)
- get big ass HDD to fit in external case
- get spare PSU for external HDD (to use upstairs for file transfer)
- get optical mouse so as to be able to naviaget PC from sofa