The last released driver for the Fastrak S150 appears to be V.1.0.20.53, A1 from https://www.dell.com/support/home/en-us/drivers/driversdetails?driverid=44m4h&oscode=wnet&productcode=poweredge-400sc. This version looks to include support for XP SP3, so you may have some luck running it with modern Windows. Keep in mind that you will have to manually extract the driver file from the installer using 7Zip, unless you have floppy disks laying around.
Windows XP X64 is not the same OS as Windows XP. XP came first, then MS used XP as a base for Server 2003 before then using Server 2003 as a base for XP 64. The reason XP64 only goes up to SP2 is because that was the last SP released for Server 2K3. Avoid XP64 at all costs.
Sounds like your mom got hold of a rare XP VLK or Volume License Key. They were intended for large corporations who have possibly hundreds of computers, essentially you would say to MS "I want a key for my 100 machines", they say "Sure, that'll be £10,000 please", you pay them and they give you a key never never expires but will only work on a VLK copy of the OS and require no activation. The idea is so IT support only need to keep track of 1 key, not 100.
If you want a Vista disc now the best way is to torrent it. I have a genuine Vista Ultimate disc and it no longer reads in a drive and from what I hear that's a pretty common issue. Download a Retail ISO with SP3, burn it to a DVD and profit. As long as you've got an AV running with real time protection theres very little chance of it infecting your main computer and as long as get one with lots of good feedback and a high number of seeds you can be pretty confident its clean.
FTR yes, FO3 does also run fine on Windows 7 but it does need some tweaking.
