Alexa remnants defy all tools: HELP

friends
by following tips here and from Castlecops, I have cleaned up nearly 200 trojans, worms, hjackers, and other from client's system. about 8 infectious agents remain, chief among them "alt.exe", aka Alexa, and a junk it spawns [browsela.dll, other].

Ewido, Spybot, AdAware, Killbox, MS AntiSpyware, stinger, Avast, and other tools find these, "kill" or contain them, proclaim victory, and move on. "alt.exe" will repopulate within seconds, with the others following over a two or three minute span. MS AntiSpy Blocks them from doing much, but they are there, resident, eating resources.

Has anyone dealt with these AFTER trying all known measures? Tips, ideas, etc welcome. My skills are pretty good [or they were..... this makes me wonder]

Zapp