With a 2900, I think every CPU that shipped in that chassis was x64, so from a hardware perspective you're fine. You're fine from a license perspective as well.
However, the media set is either x86 or x64, not both... so you will need new media. The problem is that you need OEM media to match your OEM license (at least, I assume your license is OEM) otherwise your product key won't work. You can try Dell, but they have not often been willing to ship media kits for OSes in my experience.
You might need to investigate, shall we say, "questionable" means of acquiring your media, but be aware that this comes with its own set of problems...