Without reading John's link, I would recommend at ll least 20GBs. RAM is dirt cheap. But, as Sandeep says, you can only use 4GBs if using 32-bit, of which the OS can only use 3.2 or so. So, if you have a 32-bit, you will need to change OS IF the hardware of the OS can handle it.
I hope your IT people are not charging you to reboot the server. That would be rather simple. Just watch the RAM in task manager or 3rd party programs. You should't consider 64-bit, you have to go with 64-bit.
SQL Express is only using 1GB of RAM. When you reboot, you lose the pages (not great for performance), but it frees that GB of RAM to the server for other things, which is why it starts to work better. 3.2 minus 1 gives you 2.2 which is way too little to handle the other processes in the server. I'm not sure why your IT people aren't jumping all over this.
Of course, we are assuming a lot.
