Thanks for that quests1, your mention of IE could be a big clue.
Firstly, I agree with you that 1GB of RAM should be sufficient. It is a little on the low side for Vista, so it is never going to fly along at the speed of light, but it should be plenty for normal everyday work.
Now, about Internet Explorer. Since Microsoft integrated IE into the Windows Operating System many years ago, (with IE 3 or 4), any problems with IE will often spill over into other applications, eg Explorer, (your Desktop), Windows Explorer, the file manager, as well as Word, Outlook or Outlook Express, etc.
In itself IE is OK, no add-ons, no BHOs, (Browser Helper Objects), no ActiveX components. But these add-ons get installed by web sites you visit to enhance the web site display and function and these add-ons can either get corrupted, or be poorly written, or they are malware related. I say that because anti-virus doesn't do a good job with checking browser add-ons. If the AV considers the browser is safe it leaves it alone, and so the browser is a good vehicle, like a trojan horse, for distributing malware.
So, I bet this is the reason you are having problems with application freezes. A bad add-on is causing it. If this is so, your task now, should you choose to accept it, is to test and eliminate any bad add-ons.
It's not easy. With IE open, goto Tools > Manage Add-ons, and you will see all the categories of add-ons installed. There are 4 categories, (Types), and each has a "Show" option. You could formulate a method to test each add-on or by groups, by disabling and testing.
The quicker way is to use IE's "Reset" option, in IE > Tools > Internet Options > Advanced tab, then the Reset button. But this is a reset everything option and will not only delete all 3rd party add-ons, toolbars, etc, but will also delete Favorites, History, Cookies, and any login details/password that IE has stored for web sites. You can export Favorites before using this, then import them back afterwards, but not any of the others.
I think you said you use Outlook Express, and OE also has add-ons which may also be causing problems. I don't know if it has a reset button like IE, but even if it does, I bet your AVG has installed an email virus checker plugin, so you will need to be aware of that.