As it happens, I have a dual PIII-s 1.4GHz PC with Rambus. It's got two of the last 130nm Tualatin PIII with 512k cache, and has been running XP for 15 years. Surprisingly, it's faster than many P4 machines like Matthew's especially now, long after most software compilers are no longer optimizing for P4 (PIII is P6 like Core 2, and long-pipeline P4 heavily relied on optimization, with Northwood even lacking a hardware integer multiply unit). And that's with memory bandwidth lower than many SSDs today.
XP will update itself (and MSE definitions) until 9APR2019 with the POSready 2009 updates, which obviously do not include any updates for multimedia parts of the OS like Windows Media Player (so just use VLC player). Windows 7 32-bit will actually work until 14JAN2020 but I don't have enough RAM to be comfortable running it. Windows 8 32-bit is out of the question without XD/NX-bit.
You probably won't be surfing the web on it now because those chips lack SSE2 so cannot run the current versions of Firefox, Chrome, Flash, or Office 2013. The last Firefox for no SSE2 was 45.9ESR, and the last Chrome was v34. There is a recent version of Slimbrowser that uses iE8's Trident engine, but I don't know how actually up-to-date that really is. So the only current browser that would work is iE11 in Win 7.