Viruses that just wont go away!!!

Hi

I have downloaded the following products Avast and Antivir on the anti-virus front and Spybot search & destroy, Ad aware SE, CWSShredder and Hijackthis. Hijackthis is the only one I haven't used yet, but everytime I run one of these programmes they get interrupted by I think it windows AV or something saying that one of the following was found PMS/SEARCHBAR.DLL.2 and TR/DLDR.STARTPAGE, then it gives you the option whether you wont to quarantine, delete, ignore etc and I have pressed delete everytime but when I scanned again using avast it brought them up again, I also had these 2 as well but I think they might of gone now Trojan.byteverify virus and Backdoor.coreflood dr virus, I haven't run any of these with the system restore off, I dont know whether thats important or not, have you got any suggestions how I can get rid of these buggers?

Thanks in Advance