My wife's Dell Vostro 220 is now running Windows 7 x64 and has 8 GB of RAM. I upgraded her BIOS to 1.3.0 before swapping the memory (I read somewhere that the updated BIOS supports the full 8GB).
On a related note, you can actually get the service tag out of your Dell computer in Windows by issuing the following command.
Following WMIC command will give make and model number along with service tag (service tag is IdentifyingNumber here:
C:\>wmic csproduct get vendor,name,identifyingnumber IdentifyingNumber Name Vendor ABCDEF1 PowerEdge 2950 Dell Inc.
[remote-host]# dmidecode -s system-serial-number ABCDEF1