You gave us the settings you use on other platforms, but you didn't tell us how you configured your N900. I use my N900 on the wireless setup at work (which I was involved in implementing, and Windows XP really has some issues with WPA2-Enterprise ...) without problems (with PEAP MSCHAPv2). However, it didn't work correctly if I added the wireless network from the applet, whereas adding it from Settings->Internet connections->Connections just worked without any fuss (and the additional input it requires of a manually added connection name, but it shows the list of available WLANs at the next step, picks PEAP automatically, you just need to change GTC to MSCHAP during the wizard). So, please try adding it from Settings->Internet connections. There may be an obscure bug here, and it may be worthwhile reporting.