The 150 is the same as the FX-53, not the 51, which makes it an even better deal. The 148 is the same as the FX-51 (and when I say "same" I mean that they have the same specs and performance, even though they have different names - I'm not really sure if there is actually anything different about them).
To run two Opterons you have to get the 2XX series, which is of course much more expensive per chip. To run more than two Opterons, you need to get the 8XX series which is rediculously priced (unless you are a company or reaaaalllly nerdy

).
Camara120, that test shows results from a Dual Xeon 3.2, which for what your friend is doing is about the same as a dual Opteron 250, and a tiny bit faster than a Dual 246 and quite a bit faster than a single 150/FX-53. Unfortunately, I don't know how a Dual Xeon 2.0 compares, although I imagine it would be about the same as a single 150 (if we assume that a 2.0 is 66% as fast as the 3.2) in multithreaded aps and much slower in games. However, unless she's playing lots of games, it probably isn't worth it to upgrade.
For single processor usage, the Opteron, for whatever reason, is by far the best value at the very high end. Strange how the pricing is like that. I'm guessing that AMD is trying so hard to break into the server market they need to keep those Opteron prices competitive with the Xeons, and that is why they are so much less than the FX-series. Intel just doesn't have that same advantage in the desktop enthusiast market that they enjoy in the server market. Anyway, just a guess as to whey the opterons seem to be such a good value.
-D'oh!