Yes, you can use 4 GB of RAM on a 32-bit operating system.
Yes, you can use 4 GB of RAM on a 32-bit operating system.
If Nvidia released a 32-bit version of Windows, it would change how older systems run and affect compatibility with legacy software.
Adding a GPU reduces the available RAM you have installed. The difference between the installed amount and the GPU's RAM determines if you can still use it. You may be able to use it, but whether all of it works depends on your system settings. If you have 3GB or less, you should get a 32-bit boot drive; for 4GB or more, a 64-bit boot drive is recommended.