You need to download the non 64 bit version then and install that. I had the same problem. My computers x64 so I installed that on it but the computers I use at work are only x86 (32 bit) systems. Once I installed the right one and copied the contents over to my USB stick everything worked just fine.
x64 version is the first download listed, x86 is the second one in the list:
http://code.google.com/p/sigil/downloads/list