I'm upgrading my PC from a 1.7 gig Intel Celeron, Intel 845gebv2 motherboard to a 2.66 gig Pentium D dual core and a Intel D945GNT motherboard. Will I be able to use my present DDR memory and 350 watt power supply?

Hi -- welcome to PCHF...

I am afraid you won't be able to salvage your RAM... your new board needs 240 pin DDR2 (old is 184 pin). Your PSU will probably not be enough-- though it depends on what you plan to use for video... this board has PCI express slots which can draw serious juice. I'd have to know more about what you have now.

I don't recommend you cut it too close you want to establish exactly how you will configure the new setup ... then figure out what you need for power. I'd add at least 35% to that figure for future upgrades.

you can use this calculator to help:

What Power Supply Do I Need - eXtreme Power Supply Calculator

Dual core systems need the 24pin molex power supplies. And 350 watt is very very low range now. I'd suggest at least a 500watt.