I think most ROMs support WPA. Angstrom, Sharp, and Cacko (?) are probably the ones to look at, as those seem to be the most oft used on the 5500, or maybe one of the custom 5500 ROMs floating around.
pdaXrom supports WPA and the 5500 (in at least one release), but you may want to stay away from the apparently difficult install procedure necessary to get it on the 5500. There is a guide, if that interests you.
Now for the OT question: What is a 5500g? I've never heard of any 5500 other than the plain 5500? Can anybody shed some light on this?
Anyway, hope this helps.