hmm that is odd... probably worth running a quick virus / spyware scan.
Any particular reason you have been trying to get hijackthis, precautionary?
btw I tried the first download link on the site I gave you, trend micro wouldnt allow me todo anything with firefox, argh! Anyway the second link (and incidentally the one simon gave) worked fine. So it *should* work, but who knows. If you want I have downloaded the file and will gladly mail it to you - its only just over a Mb.