@Tomalak in comments:
since ID selectors must be preceded by a hash #, there should be no ambiguity here
“#id.class” is a valid selector that requires both an id and a separate class to match; it’s valid and not always totally redundant.
The correct way to select a literal ‘.’ in CSS is to escape it: “#id\.moreid”. This used to cause trouble in some older browsers (in particular IE5.x), but all modern desktop browsers support it.
The same method does seem to work in jQuery 1.3.2, though I haven’t tested it thoroughly; quickExpr doesn’t pick it up, but the more involved selector parser seems to get it right:
$('#SearchBag\\.CompanyName');