Taken from the BFI archives.
Omniweb 4.5 – first released in August 2003 and, apparently, lost from the general web (or, at the very least, Google!) – can be found here. While the base URL isn’t an Omnigroup URL, it looks to be reasonably trustworthy as that particular file is linked to from the Omniweb 4.5 product page.
Anyway, in completely unrelated news, Omniweb 4.5 on OSX 10.3 comes to PSPB today!