Minecraft installer help - How to install mods manually into each jar?

[Delos-X]

Okay, first off, hi. First post on these forums.
I think this is the right topic, if not, sorry.

I have windows 8, with my new PC. I'm trying to install Unbelievable shaders mod to 1.2.5. I need to use this installer since my 1.2.5 clean jar has gone missing.
If you can point out where the jars are held, I'll be able to do the rest, thanks.
Any extra info needed, just ask. ^^

 

[supercity]

If your using the launcher to downgrade, then the old jar files will be in the same place as the minecraft.jar so; /.minecraft/bin/minecraft<Version_Number>.jar