It is virtually impossible to get Vista 32-bit software to recognise 4GB of RAM.
It wasn't until I bought 4GB that I realised how well known this problem is and it is also acknowledged by Microsoft who offer a workaround, which wouldn't work for me - luckily - as it reduces the efficiency of the RAM.
I Had a PC with 2 x 1GB of RAM fitted and bought 2 x 1GB extra only to find that 3GB was recognised.
I tried various configurations but could not achieve more than 3GB.
I was left with few options:
1. Take out 1GB and run the PC on 3GB. Sounds good but in fact it's not because if you don't have RAM loaded in pairs you end up with the DDR dual channel disabled.
2. Leave 4GB in and get 3GB usable with DDR dual channel enabled.
3. Update to 64-bit Vista which will recognise 128GB RAM.
I went for number 2 as I had already paid for the RAM. I might one day get a 64-bit o/s or Vista SP1 might contain a fix.
If you want a bit more info have a look at the Asus Forum, where you will find quite a bit about this subject. click here