Disabling the antivirus when installing new programs is not only unnecessary, it is probably even completely wrong advice. You need the antivirus most when you are installing new programs onto your harddrive. It will help you prevent installing malware (virus) that you mistakely downloaded instead of the real program.
You may safely ignore this advice, Internet Explorer 7 Update installs just fine with avast! running. (as pretty much every program should).
In case you would really need it, you can right click the (a) icon in the tray (where you clocks are) and choose "Stop On-Access protection", but don't do this when installing new programs, especially when you are not 1000% sure they are from trusted source (and you can hardly ever be sure).
The PDA stands for Personal Digital Assistent, palm or iPaq of whatever else, certainly not your PC. Never mind, perhaps the moderator might move this topic to the "avast4 Home/Pro" forum.
Cheers,
Lukas.