Here's a very late reply but hope it could help a few frustrated souls...
Situation: I upgraded my laptop from 1GB to 3GB (1GB + 2GB config), did so by inserting my new RAM into slot 2. BIOS and sys prop shows 3GB, but Task Manager only shows 894Mb (~1GB). Tried putting the 2GB RAM into slot 1 and the old RAM into slot 2 - no use.
Solution:
1. Power off computer.
2. Remove ALL RAMs from all slots.
3. Insert the 2GB RAM into slot 1.
4. Start computer and check memory in Task Manager (mine said about 2GB)
5. Power off computer.
6. Insert the 1GB RAM into slot 2.
7. Start computer and check Task Manager - hopefully it shows 2831MB.
Cheer up, you haven't wasted your newly bought RAM