Hi Mohammed,
Settings for star trails and timelapse really depends on what effect you are after and what camera equipment you have. You mention that you want to do a star trail AND make a timelapse movie out of the images as well. If you want to do this, then you need to keep the individual images to an exposure length that does not produce a noticible trail. To do this, use the 600 rule to determine the maximum shutter speed before stars begin to noticibly trail. The 600 rule is 600 divided by the true focal length of the lens. You are running a canon crop sensor on the 40D so the true focal length of your 17mm lens, is 17 times 1.6 = 27.2mm true focal length (so yes it isn't really wide to answer another of your questions. You need a true focal length around 20mm to start getting 90 degree field of views) So 600/27.2= 22 seconds maximum shutter speed if you want to do timelapse movies and star trails like these couple of mine
http://youtu.be/62G4RyGttVo and
http://youtu.be/QBobahkww78. Once you know the shutter speed then you just need to work out what ISO and aperture you want. If you are doing timelapse then you generally want as much star light as possible, so high ISO's and wide open apertures. Don't worry too much about noise with high ISO's. It gets masked somewhat in the final vid. On that note. Turn off in camera noise reduction. It is why you are getting the gaps inbetween shots. The camera is taking a "dark frame" after every image if it is left on. For star trails you need seemless trails, so set the camera for continuous shooting and lock down the shutter button with a timer remote. I have no experience with using EOS utility to take the images. You should be able to pick up a timer remote for your camera for under $40 on ebay.
http://www.ebay.com.au/itm/LCD-Timer...item27bb2a991a <- for example (i use this exact one)
If however you just want a star trail image then you have a lot more flexibility in the camera settings. You can go longer exposures to reduce the overall image number. You can go lower iso's and higher apertures to reduce the number of stars picked up for a more subtle effect.
A couple more of my examples
http://obsidian2010.deviantart.com/a...ping-286876074 <- high iso for a star filled sky
http://obsidian2010.deviantart.com/a...Dusk-199733117 <- lower ISO for a more subtle effect
Other camera setting are detailed below the images. I have a number of other images on that site as well. If you go to my profile and then click on gallery you should be able to find all my star trails there somewhere. You will be able to see what settings I have used for different effects.
One last link:
http://www.naturephotographers.net/a.../fv0509-1.html This is the best online article I have seen on capturing star trails. It tells you everything I have said and more.
Hope this helps.
Cheers
Greg