An earlier discussion of eBay resellers selling Win2003 Enterprise copies centered around sales of "NFR" (Not For Resale) copies, which is clearly illegal. However, there are copies of Win2003 Enterprise P72-00818 being offered for sale that the sellers claim were promotional copies that have no resale restriction nor are time-limited or function limited licenses. The only difference seems to be the part number P72-00001 vs. P72-00818.
I am planning on running multiple instances of guest OS's under VMWare, and as such I'm running my memory up to 6GB and may go all the way to the 12 GB that my Dell PE 2650 will accept. My use is for development and test, not production operation, so I plan to use VMWare Workstation rather than VMWare Server, which I realize comes in a Linux version that supports extended memory, but at $2500 I think I'll go with Win2003 Enterprise and Workstation.
Note that I realize that these are not R2, but I don't need R2, only the extended memory available under Enterprise.. Release 1 is fine with me.