Currently Installed Memory: 1024 MB
Available Memory Slots : 3
Total Memory Slots : 4
I guess you now have 1 slot filled with 1 1024MB strip and got 3 slots left.
Maximum Memory Capacity: 4194304 MB
4096 GIGABYTE? On four banks? Thats 1024 Gigabyte per bank!
I doubt there are 4096 GB slots available yet, so by best guess is you actually meant 4096MB slots. (=4GB slots).
So, in this matter you can install 4 x 4GB = 16 GB maximum.
Since you already have 1 1GB slot filled, my advice is to fill all the others with 1 GB as well, resulting in 4 x 1 = 4 GB. Pleny for a normal OS.
If you want more however, i advice to go for adding 2 x 2GB, in total resulting in 5GB (2 x 1 + 1 x 1). This way you have still one slot free for extra memory.
Consult your manual on which memory capacities, slot behaviour and memory types are supported. Before you buy anything, open up the computer and check if there are actually really FOUR slots. Sometimes motherboards tend to see 1 slot as 2.