Pherim: That should both be possible without any problems. In fact, Music is really easy because it is not even inside a BSA but just in the game's installation folder. Replacing these files (in Data\Music) with files of the same names is already enough for them to be played in the game.

Voices and sounds may be a bit more complicated. First, you have to extract the BSAs in the Data folders to know which files you want to replace. This can be done with BSA Browser (yes, that is a Fallout 4 mod page, but it can open BSAs from all Bethesda games since Morrowind).
The BSAs you are looking for are Fallout - Sound.bsa and Fallout - Voices.bsa. Extract them to a location of your choice (but better not the Data directory itself) to have access to the files inside. To replace the sounds in the game, you have to create sub folders in the Data folder that match the subfolder in the BSA, for example Data\sound\fx\amb, and then place files with the same names as the sounds in the BSA in these folders. The game should use them automatically (although you'll probably need this to deal with an engine bug that prevents replacers to work in Fallout 3).

It may work similar with voices, but I am not sure about that, as the voice files come with .lip files which make NPCs move their lips correctly while speaking. If you only replace the voice files the game would still use the original .lip files and it might work, although it could be a problem if the sounds have different lengths and also the lip movements would possibly not be correct any more. I read that .lip files cannot be generated in the Fallout 3 GECK for some reason, which is why the Oblivion Construction Set has to be used for that, although I found this video, which might help you with that: https://www.youtube.com/watch?v=qVFr20Nf0Ws

Pherim: That should both be possible without any problems. In fact, Music is really easy because it is not even inside a BSA but just in the game's installation folder. Replacing these files (in Data\Music) with files of the same names is already enough for them to be played in the game.
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Voices and sounds may be a bit more complicated. First, you have to extract the BSAs in the Data folders to know which files you want to replace. This can be done with BSA Browser (yes, that is a Fallout 4 mod page, but it can open BSAs from all Bethesda games since Morrowind).
The BSAs you are looking for are Fallout - Sound.bsa and Fallout - Voices.bsa. Extract them to a location of your choice (but better not the Data directory itself) to have access to the files inside. To replace the sounds in the game, you have to create sub folders in the Data folder that match the subfolder in the BSA, for example Data\sound\fx\amb, and then place files with the same names as the sounds in the BSA in these folders. The game should use them automatically (although you'll probably need this to deal with an engine bug that prevents replacers to work in Fallout 3).

LOSTSOUNDZ: Im not trying to code or mod i guess,just replace assets (sound)with my own creations.I guess i looked at Fallout 3 becuase i love the game and it would certainly be step up fro the size of game i have worked on before.
Do you know if you can also replace the voices of the characters aswell as sounds and music in Fallout 3?

Lin545: Lin545: Pherim is spot on, the engine will prefer external files to ones inside the archive. So you just need a file with same name and the game will replace it. The other way is to make a patch that changes which file is played for each event using GECK, which is much more time consuming.