Hi, i'm thinking of upgrading my PC from AGP to PCI-e and running an x1800XT (with the possibility of Crossfire on the horizon). my current power supply is a thermaltake 420W, 20-pin connector, single 12V... i.e. outdated technology where PCI-e motherboards and SLi/Crossfire are concerned. i'm running one optical, 1GB ram, and four HDDs. this PS clearly won't accomodate 2 x1800XTs, but if i avoid Crossfire for now, will it likely be able to accomodate a new PCI-e MB and the x1800XT, or do i need to upgrade it before i upgrade the rest of my components? how important are dual 12V rails and the 24-pin connector? in addition, many power supplies on Newegg are listed as "20+4 pin" - what does this mean?