Always make a backup of your game folder before installing custom files. It's recommended to use a separate install to avoid file mismatch errors when joining multiplayer servers.
All the old maps and mappacks are repacked to separate files and contain all required packages in each download. The reason for this is that allot of maps had bad files overwriting official files, different files with the same name, different filetypes with the same name (Textures/Sounds etc), http redirect incompatible characters in file names, corrupted archives and many more things that all have been fixed and repaired to make all maps playable from one package collection.
Due to the problems described above, it is not recommended to mix maps and files from other sources with the maps you downloaded from tactical-ops.eu, as bad files can cause conflicts with eachother and make maps unplayable and give file mismatch errors.
When installing large amounts of custom maps (1000-1500+) it might take anywhere from 30 to 60+ seconds to open the practice session window, it gets worse the more maps you add. Up until 2000+ maps then it crashes when opening. So its not possible to install all custom maps at once.
To install them simply drop the archive in your TO folder, click "Extract here" and the map is installed with all files in the required folders. If possible the original readme files are preserved inside a folder "Readme/Mapname/" to prevent clutter. However very unlikely, if you ever find a Custom Map that is somehow missing a package in the download please notify me with an email. Most likely you can find the missing files in the Public Redirect in uz format.
Since almost all old TO Mod maps are converted and fixed to work on TO3.4 & 3.5, they are no longer stored in the File Archive to prevent people getting bad files in their installation. Same reason as why all the mappacks are no longer available for download. If you are looking for the original TO Mod maps to play on UT99 you can find those in the Unreal Archive. The original SWAT maps can still be downloaded from the Other section in the File Archive.