Hey, thx for all the replies.
First off, I'm sure anyone who has played more than once realizes turrets are no good on their own... I hesitate to even leave two together even if the aliens are on s2.
I like a least three (in a triangle formation), preferably more. And when I mentioned repeaters, I mean so that you can build turrets guarding the hallways that lead to the room that your base is in. (Usually, not more than two, thank goodness.) I think the best way to do that is to have the turrets able to fire at the aliens whilst they charge up the hall at them.
However, based on your responses, I paid attention next time I played... I can see the point about the aliens charging past them, as they often do. The problem is, IMHO, the turrets damage sort of sucks vs the larger aliens, and the turrets have a ridiculously short range. (The alien is on the other side of the room, for goodness sake, you might want to bloody well
shoot it!.. I can now see how aliens are able to overwhelm/jump over the turrets: they don't fire until it's too late!
I have linked videos so those of you who have high speed can see how I set up a base... however, PC$Sundance entered the game, and said he had better ideas, and since I"m a n00b, I let him take over; the last vid is of his setup. (Not bad... but the aliens still won. I'm sure they would have with my setup just the same... :p

)
Oh, and the reason I have turrets out away so far is to prevent the aliens from getting
anywheres near the base, which, as I now realize, is useless; the only reasonable option seems to be to have a few crack shots in a halfway decent assault team. The thing I notice is the aliens like to take down 1 or 2 vital structures, (armoury, medistation) then leave before they can be killed (this is when someone else is building; my method just seems to delay them for like 2 minutes... no use) and of course if they get the reactor down, you might as well bend over and kiss your ass goodbye, unless you get lucky or the aliens aren't all competent.
And, of course, I would prefer to have a two or more tiered defense, with turrets guarding the hallways leading to the base, (4+ to each), turrets guarding the doors / entrances themselves (2-3+ each), and maybe 5 turrets, preferrably 8, mixed in with or closely surrounding the base. But the BP's always seem to suck. (lol even for the aliens; I never am comfortable without three acid tubes over every door, + two on the sides, and a trapper(s) on the ceiling over the doors).
It would seem that the BP (and time limits) on most servers is geared toward Halo-style combat, with less emphasis on strategy; just make sure your base can't be immediately nuked with one rush and you've done a fine job.. hmph.

These are around 5 MB each:
http://files.filefront.com/tremulous_1_2007_04_08_190avi/;7185981;/fileinfo.htmlhttp://files.filefront.com/tremulous_1_2007_04_08_191avi/;7185982;/fileinfo.htmlhttp://files.filefront.com/tremulous_1_2007_04_08_198avi/;7185983;/fileinfo.htmlhttp://files.filefront.com/tremulous_1_2007_04_08_190avi/;7186107;/fileinfo.html