Correct - Vista wants 3 GB of RAM minimum, to run semi efficiently. With 4 GB of RAM, to make use of all 4 GB, you'll want a 64bit version of Vista.
However, Roy, the main problem here is that this board only supports 2 GB max -
1stChoiceMemory.com - MSI 661FM3-L Motherboard RAM Memory Upgrades
Furthermore, it supports a small variety of CPUs, as seen here -
CPU-Upgrade: MSI 661FM3-L (MS-7082) cpu support and features
Finally, the board is so old it simply may not work - you'll want the absolute latest BIOS made for the board but even that may not be enough.
Twilightluke, by the time all is said and done, you'll put more money into upgrading than you can getting a decent quad core machine with 4 GB of DDR2 RAM and a decent sized HD for about $600 USD:
Newegg.com - $500 - $750, Core 2 Quad, Desktop PCs, Desktop PCs, PCs & Laptops Intel Core 2 Quad Computer, Intel Core 2 Quad Desktop TigerDirect.com