All Core 2s have EM64T support.  However, the chipset in the system is too old to support memory remapping - so you will not see all 4G of RAM, even with a 64-bit operating system.  
About a month ago I purchased two 2GB ram modules from Dell to replace the two 1GB ram that shipped with the notebook.  I was less than thrilled when I bought the 1210 when about a week or so latter it was replaced by the XPS 1330—late June 2007.  I was well-aware of the 32-bit OS limit of a bit more than 3GB ram usage (upgrade to Vista Ultimate 32-bit), but I thought the processor (Intel Core 2 Duo 2.15 GH) & other hardware would support a 64-bit OS.  With the NVIDIA GeoForce Go 7400 display adapter, however, I’m not really confident that a 64-bit Win OS is supported. No issues with the new ram per se—you just need to be a bit patient for the BIOS (Dell ver. A08) to recognize it.  Other than the video card, I don’t think there are other 64-bit hardware issues.  If anyone has any experience trying to use a Win 64-bit OS with the XPS 1210, I’d greatly appreciate the feedback. 
XPS 1210 Notebook & Win 7 64-Bit OS