Titan p4 667 series gigabyte motherboard

According to this list on GigaBytes homepage
http://www.giga-byte.dk/Support/Motherboard/CPUSupport_Model.aspx?ProductID=1406
You'll be fine for quite a while, until the 478-socket processors are available in stores.
Your motherboard supports much faster CPU's than your current Celeron, so if money is short upgrade our processor.
But if you want to secure your motherboard for future upgrades, then I suggest you get one that support the newer dual-core processors, and PCI-Express instead of AGP.
Allthough you can still get pretty good GFX-Cards on the AGP-standard the PCI-E standard is the future.

I hope this answered your question :-)