Memory Upgrade for Dimension 1100 (DE051)

Dell Dimension 1100 computer came with 512MB of DDR PC3200 400 MHz memory (2x256M). That was fine when it was new, but with the increase in size of Windows (XP Home SP3) and AVG antivirus program there is now so little free memory that it has slowed to a crawl. So I have to upgrade memory.

It appears that each of the 2 memory slots can hold a DDR memory card 256M, 512M, or 1G. It should run a little faster if both are identical but mixed should work.

I didn't want to throw away both existing modules. I tried store brand memory from Staples, PC3200 1GB, in one of the two slots with the other slot either empty or the factory 256M, and the machine won't boot; the beep code indicates a memory problem. Two different ones behaved identically, so it is not likely just a bad memory stick. Another posting in this forum says that others have seen this with Kingston ValueRam. It was suggested there that ValueRam and other similar generic memory should always be used in matched pairs. There was no final posting to indicate whether this actually solved the problem.

Strangely enough, a Staples store brand 512M module, same specs as the 1G module that fails, does work. But that gives only a total of 750 MB which is better than before but I would rather have at least 1G total.

So I am considering two main options: Kingston premium quality 1G module in mixed configuration, giving 1.25GB total, or two Kingston ValueRam 512M giving 1 GB total. The price is similar either way. Has anybody tried either of these options?