How to insTall antivirus when virus is blocking installation?

hai guys.actually i do have experience in dealing with viruses but still im in the process of learning advanced ways to beat it myself.i have removed many dANgerous viruses from my pc in the past without formatting it.i learned about the way these viruses work and removed them with a combination of some tools.however now i have new viruses which got into my pc from a memory card.firstly this virus corrupted many of my programs and made them unaccessible with an error message.but i tried a few methods and finally i cud access these programs.actually the path of the programs shortcuts were missin or deleted by the virus.now i need help on installing spyware doctor coz this is the software that has always saved my computer on several occasions.by the way when i try to install spyware doctor an error message comes up "runtime error (at 529:1227): out of range".when this error message showed up, i thought ok the setup file might be corrupted by the virus,so i decided to download the same spyware doctor setup again so that i can install it,but after i downloaded the setup again,the same error message showed up.actually i forgot to mention one thing also.when i tried this setup,always the error message showed up but once i between i did something which i dont remember and the setup did work in between without error message but i did a foolish thing by aborting the installation by mistake,later it never works.plz help.i have many tools for monitoring my pc processes and im familiar with all the processes.i always end processes which im not too familiar with thats how im able to connect to the network coz the virus was blocking my network also