Must be an onslaught. From what I've read, these types of programs (described above, about:blank, etc.) have 2 dll's in Windows registry. One is hidden, or 'invisible'. When you have No-Adware, or Ad-Aware, etc. search and destroy, the hidden dll is left. It's function is to restore or regenerate the missing (cleaned) dll whenever you reopen your browser.
There is a 'manual' fix, which is moderately involved and rather than trying to explain it, do a search for, eg, the about:blank fix.
However, the only ones I found were for XP. I don't know whether they're applicable to 98 or not.