I use a biostar MCP6P M2+ micro atx board, and it runs most am2 and am3 cpus that require 95 watts or less. If you want to run a cpu at higher wattage, checkout the micro atx 785 chipset boards. You may have some problems if your windows installation is tied to an acer bios chip. Try running cpuid to see what brand motherboard your acer uses. Even with backup dvd's of xp or vista, they might not work without an acer identification of the bios. My hp backup disks wouldn't work on a non hp motherboard.
Any AM2+ micro ATX board will do just fine. You want to be sure that you can upgrade your computer in the future so make sure you get a board that can support AM3 CPUs. Measure the dimensions of your current motherboard to make sure that your case isn't too cramped as there are a few boards that claim to be micro atx but are a little wider which will affect your ability to put it into cramped cases like your acer is likely to be.
Also add another stick of RAM. Likely you have a single stick of DDR2. Adding another of the same speed will allow the RAM to run in dual channel mode which will boost your performance in addition to having more memory for your applications.