Do you mean SpywareBlaster AND SpywareGuard? Easy. And I also have SuperAntiSpyware, MalwareBytes and WinPatrol. That is my antispyware choices.
Unlike antivirus programs, which can have only one installed at a time, many people recommend more than one antispyware program. Some, like SpywareGuard, watchs in real time for any suspicious behaviour by malware while others watch for signatures.
Some are specialists, looking specifically for trojans, keyloggers, or rootkits.
So,hopefully you can see why more than one is just good insurance.