I´ve got this really old projector that i want to connect to my xbox. I have read alot of posts but just get confused by all the diffrent video standards.

The projector has got 4 BNC-connections marked "R", "G", "B", "Sync", two BNCs that are marked "video" and two s-video inputs. It also has a switch where you can choose between "RGsB analog", "RGB/S analog", "super video" and "video". I guess RGsB means sync on green.

so my idea is to buy a xbox RGB cable with SCART output and connect the RGB out-pins on the SCART to the R,G and B input on the projector. Will this work? Or should i connect something to the SYNC-input too? Do i need a VGA-bios? should i buy the HD-A/V-pack instead of a cheaper RGB cable? or maybe i could use the standard cable that came with the xbox?

So many questions... i would be very happy if someone could help me with some of this.

You'll need to wire the composite video output to the sync BNC on your projector.Being a tv I expect it will be able to strip the sync off of composite video.If not you'll need a sync stripper such as the lm1881,check out www.gamesx.com for a circuit.Wire the rgb lines to the respective BNCS,as you said .If your tv supports progressive which it most likely will unless it is an old one you'll need to either :
1.Get an x2vga or equivalent or build one yourself
2.Build a vga mod and use a vga bios,will only work on sub-1.4 boxes.Your projector will need to either support sync-on-green(projectors often do),or you will have to strip it down to composite sync or horizontal and vertical sync(lm1881 can do both here).Also you might not be able to use progressive mode through the bncs,does your projector have any other inputs such as a vga port? Best to check your manual if you have it or look on the web for details on what it supports....and then just check sparingly,you don't want 31khz running through if it can't take it as it can damage the projector.You'll probably see a double image or something similar if it is a 31khz picture running through a 15khz port

EDIT: Most likely it won't support progressive since you said "really old",but there is still a chance if was a high-end machine back in its day.Just try wiring up a scart lead to start with and see what happens.

or he could skip all that trouble and buy a composite to s-video adapter for like $10 on ebay

Thanks for the replies. The projector is from 1989 i think so i probably won't find a manual online... and no VGA input. it has got a switch for "fast sync" or "slow sync" has this got to do anything with the 15 or 31 KHz? (progressive or not?) .

I guess i could use the s-video input but i've got these really long coax-BNC-cables that came with the projector that i want to use, and of course i want to have the best quality possible. ( if its not too hard) .

so i will do like this:

Xbox->RGB-cable (SCART out)->R,G,B pins on SCART to R,G,B BNC,
composite pin to sync BNC.

if my projector don't have progressive scan and i connect it like this, will i need the VGA-bios?

Superior to S-Video sounds good enough plus i understand that HD only works with NTSC games, and i live in europe so most of my games are PAL. and i have got some trouble getting into the MS-dash to change HD-settings after installing a new HD, so i think standard RGB is enough.

Before i start to build this i have one more question. Do i have to separate the R, G and B grounds or is this the same ground (connected internally) ? i wonder if i can put all BNCs on the same metalplate without blowing anything up..

S-Video to RGB is not as big a leap as say composite to S-Video, so marginally superior would be more accurate. Don't let that fact that your games are PAL put you off setting your console as NTSC, 99% of the PAL games work fine and with Enigmah, it is very easy to switch back and forth. Getting into the MS Dash maybe your biggest hurdle with your drive.

Don't know about your RGB cable build, there doesn't seem to be any bridging at the SCART end of my RGB cable, but I don't know about the AVIP end?

Almost done now, i've done a quick test with the projector, (first time i've used it) It looks good but i get these horizontal lines moving up and down, like shadows (not lines ontop of the picture) The color and sync works fine though. Could the lines be caused by my connection or is the projector bad? I want to attach the projector to the ceiling but not if something is wrong (it's really big).

I checked the ground points with a multimeter and they dont seem to be connected. The voltage is zero across them though (with the xbox on) so maybe you can connect them anyway. I think the most logic thing would be to mount all conectors to the same metalbox to get good sheilding but im not sure about this.

Anyway, thanks to everyone helping me out with my badly written newbie questions. It has really helped me alot.