Seconded Wine (I'd suggest installing from the repositories with `sudo urpmi wine' rather than manually downloading, but they should be equivalent). I believe that the most recent Wine versions can succesfully install the full trilogy and their patches (you might need to
windowed mode, though).
Ensure that you can start the game by this point.
I don't think you can execute the classic (non-WeiDU) baldurdash installer, but you can ask somebody for a copy of their dialog.tlk and override. Don't install it by this point, merely unpack it in a subfolder of your bg2 folder. Vlad's WeiDU Baldurdash doesn't have this problem ("merely" the standard WeiDU issues).
If the mod is a zip or rar, uncompress it in your bg2 directory. If the mod is distributed as a .exe, you can use `unrar' to unpack it; if that fails, run the installer (with windowed mode) and refuse to install via WeiDU.
Not all WeiDU mods have a Linux version. Mods without .bat files in their folders can be simply installed; otherwise, you have to translate the .bat to .sh (Amber for Linux on G3 has examples of all required operations, if you need more instructions I'll oblige).
While using wine to run weidu does sometimes work, you should really use
WeiDU for Linux instead. From the archive, unzip WeiDU, WeInstall, tolower and tisunpack to somewhere in your $PATH (/usr/local/bin) and install the oggdec and sox packages with your package manager (they should already be installed, but just in case...).
Run tolower from bg2's main directory, answer yes to all questions.
Now you can install non-WeiDU baldurdash by overwriting dialog.tlk and the override.
Install mods via `WeInstall tp2-identifier' (`WeInstall nej2v691', not `WeInstall setup-nej2v691.tp2').
Finally, if you installed on ext3, install
my biffer utility.