You are correct, Spybot S&D is a good prgoram and is free. Housecall that you mentioned is owned by TrendMicro and is a free online virus scanner. They would like you to buy the TrendMicro antivirus program but it is not necessary to do that in order to use the free online scan. This list here are some of the free ones that we recoemmend here. You already have the first one as long as you did not get a ripoff by mistake, there are many out there. Make sure that the one you have is the same one on this list.

Spybot S&D (download, check for updates, read the tutorial and scan often, it also does some blocking)
http://www.safer-networking.org/en/home/index.html

SpywareBlaster (a blocker only, download it, check for updates, enable it and leave it alone except for checking for updates occasionally)
http://www.javacoolsoftware.com/spywareblaster.html


SpywareGuard (similiar to SpywareBlaster but works in a different way and does not update as often for that reason.
http://www.javacoolsoftware.com/spywareguard.html

Ad-Aware SE (a scanner, download, check for updates, read the directions and scan.
http://www.lavasoftusa.com/

cwshredder (stand alone unit)(another small scanner for certain things, ALL other windows should be closed)
http://www.intermute.com/spysubtract/cwshredder_download.html

Also do an online scan at one or all of these.
On the first one, make sure you checkmark the box that says "autoclean"

Housecall (using IE with Active-X)
http://housecall.trendmicro.com/housecall/start_corp.asp

Housecall (all browsers using java)
http://uk.trendmicro-europe.com/enterprise/products/housecall_launch.php

PandaActivescan
http://www.pandasoftware.com/activescan/com/activescan_principal.htm