I recently subscribed to a brief subscription of A-Squared because my ISP adamantly suggested it due to my computer sending 'bounce/spam e-mails' at the most random of times unbeknownst to me... I had bad experiences with this program in the past on past PCs, but could the in-effectiveness of this program crash a seemingly fine harddrive?

As with all anti-virus/anti-spyware/malware,etc programs, they all claim to be superior and promising of the detection of such 'threats' to your system, but just out of curiosity, what is the efficacy of this particular program? I was also recommended to use this in conjunction with MalwareBytes (HDD crashed soon thereafter)...Any links to the seemingly inevitable BSOD/Crash?

Since the installation of the new HDD, I again have A-squared running on my system as the MAIN "anti-everything" program, but I'd like to know what is the most compatible to my newly revived computer?

PC Model/Type: HP ze2000 series
OS: Windows XP PRO
* Also, SVP3 was recently installed*

^Not sure if the above mentioned info is necessary...

Any/All advice is kindly appreciated!

I don't think there is any program that is more or less compatible. There are defiantly good and better antivirus programs. I would recommend Microsoft's own Internet security program:- http://www.microsoft.com/uk/security/default.mspx
I am running it with Comodo firewall, Malwarebytes and Spywareblaster.
If you ask here you may get a lot of different ideas about the best as they are all very similar. None are perfect.