The World of Avlis

If I replace old NWN files with the Avlis ones can I still log onto other servers or will the files not work?

which files are you refering to?

the ones that the hakpak replaces and you have to back up

Hakpaks don't overwrite files, that's the point of using them.

Instead of having to replace Bioware's content with customized stuff the creators of mods can put their customizations (replacements and additions) in to a hak pak which is manipulated as a single file and only extracted to memory (and perhaps the nwn/temp directory?) when called for by a specific module.

Avlis does use a modified version of the dialog.tlk file, however which you want to make sure you back up before replacing... I believe the Avlis one is compatible with the single player campaigns, but you'll need the original in order to do updates from Biowares update engine and perhaps if you decide to play on another PW or online server... As far as the hakpaks go, though, don't sweat them, they are harmless as long as you use them as they're intended.

The dialog.tlk does not, to my knowledge, actually overwrite anything, but adds to it. It has worked fine on the other (admittedly, one) server I have tried it on just fine. If another server used a custom dialog.tlk, THEN things might start getting hairy...