Might be that you managed to get a build that needs shift key + right mouse button (=extended context menu, as known from Vista and Windows 7) to see the thg cmenu entries. Inside repos, the thg cmenu is shown with out shift key.
They changed that later. So in newer builds you will probably find everything as it was before.
I think this doesn't need a 32 bit machine :). Rather the contrary. Maybe I'll look into it (very low prio though, feel free to beat me to it).
Hypothesis: GetTHgProgRoot() from TortoiseUtils.cpp tries to read the install path from Software\TortoiseHg from the registry, which the installer most likely writes to the x64 areas of the registry, but the x86 shell extension reads the 32 bit registry, which most likely doesn't have that entry.