Q: There's only one savegame?
A: Yes. But, depending on what version you have, there are one or more backup files. When you save the game with either Ctrl-S or the Esc key menu, any previous save is renamed as a backup.
If you have v2.0 - the version that comes on the CD - or v2.1, there is only 1 backup file. That means the previous savegame is retained, then overwritten the next time you save. v2.0 and v2.1 backup files end in .bak
V2.2 introduced a new system. By default, there are now 5 backup files. Each time you save, each of the existing files are renamed and if there was 5 files the oldest one is overwritten to make room for the newest backup. The savegames are numbered 1 thru 5.
However, there is a way to increase this number (but then also increase the hard drive space that eventually savegames take up):
If you add
max_save_backups=(x) where (x) is a number
to the command line in your DS2 shortcut, then you can have (x) number of savegame backup files.
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Q: I screwed up and saved but I don't want the save. Can I "back up" one savegame?
A: If you've only saved that once, then yes. The game makes at least one backup copy from your previous save. But you'll have to manually replace the savegame files for the game to read the backup.
The savegames are kept in My Documents\My Games\Dungeon Siege 2\Save. There is a Multiplayer folder if you play LAN or Internet, and a SinglePlayer for single player. In both cases, the folder contains a folder inside of it with your character's name.
For this example, I'll use Single Player and a character named "Bob":
If I go into \My Documents\My Games\Dungeon Siege 2\Save\SinglePlayer\Bob, I will see at least two files:
Bob.ds2party current party savegame
Bob.ds2radar current world savegame
If I am running DS2 v2.0 or v2.1, and have saved at least twice, then I also have
Bob.ds2party.bak previous party savegame
Bob.ds2radar.bak previous world savegame
These are the previous saves. So, if I delete the Bob.ds2party and Bob.ds2radar (you would first make a copy of the Bob folder, just in case, right?), then rename the .bak files so they don't have the ".bak" part, then they look just like the ones you deleted. DS2 will load them up.
If you have DS2 v2.2, it has been adjusted to allow up to 5 backup savegames. So, instead of the .bak files, you have:
Bob.ds2party.ds2bak1
Bob.ds2radar.ds2bak1
Bob.ds2party.ds2bak2
Bob.ds2radar.ds2bak2
etc...
".ds2bak1" are the most recent backups, the ones that were the current savegame. So if you rename the .dsbak1 files then you'd get the party's previous save.
Gamespy files cannot be manipulated like this. Although there is a local copy kept on your machine, the savegame is actually stored on Gamespy.