add 2GB (for 4GB) RAM? have 32-bit winXPhome, GA-MA69G-S3H board

Hi all. I have 2GB of physical memory in my computer running Windows XP Home (32-bit). I'm quite frequently exceeding the 2GB (at least in the Page File info in Task Manager). Would it be a good idea to get another two 1GB modules (in a dual-channel kit) so I have 4GB? I'm aware of the <4GB memory limitation in 32-bit Windows. My motherboard is a Gigabyte GA-MA69G-S3H, and the on-board video is currently configured to use 128MB. (I may consider bumping it up to 256MB, but no higher than 512MB, and ONLY if I add more physical RAM. Getting a dedicated video card will likely happen in the future, but is not an option for at least the next several months.)

So should I....???
get 2x1GB (2GB) - have a total of 4GB
get 2x512GB (1GB) - have a total of 3GB (and thereby hopefully not have to worry about the memory limit, although I'd rather not use this option)
get 2x2GB (4GB), and remove my other 2 1GB sticks, and still have 2 slots available (other 2 options all 4 slots would be full. I don't plan to get a 64-bit Windows until Windows 7 comes out, and even then if there's still 32-bit W7 available I may use that instead for backward compatibility, AND I don't know if I'll be attempting to install it on this computer.)

This = the RAM I currently have installed. Is it ok, for the second 2 sticks, to go with a different brand/spec/whatever, or should I get 2 more of those?

The less I have to spend, the better, but I'm not looking at the absolute bottom of the barrel. I just don't want to spend $50-60 for memory modules when something for $30 would be just fine. (I do want decent quality memory, though, and I believe getting ones with heat spreaders would be good.) Also, I don't do mail-in rebates, so don't factor that into the cost. (For example, if a particular set is $59.99 with a $35.00 MIR bringing it to $24.99, the cost, as far as I'm concerned, is $59.99, NOT $24.99.

What would be the least expensive of these 2x1GB dual-channel DDR2-800 kits that you guys would recommend?

I often open a lot of photos in GIMP, quite a few sounds in an audio editor, and I'm starting to get into video editing. (I'm hoping to buy a Canon SX1 IS digital camera next month (although I'll have to import it from the UK or somewhere cause it's not available in the USA) which shoots 1080p video.) I'm not a hard-core gamer, although I do play quite a bit of Team Fortress Classic (and as far as I'm concerned my system runs it just fine) and a little bit of Fortress Forever (a Source engine mod), which I can get by with. Usually my main memory hog is Firefox. I've had it using over a GB, and of course that's with other programs running at the same time too.


Also, on another note, I'm often having problems with my Avast web scanner. Every so often (typically every few days or so) AshWebSrv.exe (or it might be Sv not Srv I forget exactly) will spike my CPU usage to near 100% solid, and render my web browser useless. I've heard the problem linked somehow to Firefox, which I'm not about to dump. When it does this, the only cure is to restart my computer. Is there any way I can fix this? (I'm running the free version of Avast, and previously had been running the free AVG.) I don't like investing more than a small % of my computer budget on software, and I already have exceeded that quota with Windows XP.