as far as i know, windows 7 32-bit can only use/work with 3gb of memory (in your case 2.9gb)
upgrading the mobo bios to the latest version won't help either.
For you to utilized the 4gb you have, you must use the 64-bit version of windows 7, but even with win7-64bit, i've read some users are also having problems and their system could only recognize 3 gb max