The only lens i use for these types of shots always had the infinity marked- I would imagine that youll need to find something to focus on at about a 40-50yard out mark and then aim up at the sky.
14-24MM
400 ISO
68Second Exposure
These arent great examples-but this lens has an infinity mark, and thats what i used, with a remote cable timer. (i'd love to have an intervolomter, maybe next year, ill buy one)
http://farm7.static.flickr.com/6086/6080325792_67061ee9e3_z.jpg
Stars, Boats and Pool Glow by Lucky Lola Studios, on Flickr
Same Lens/ISO
24second exposure.
http://farm7.static.flickr.com/6065/6079788665_0c26d43965_z.jpg
Stars, Boats and Pool Glow by Lucky Lola Studios, on Flickr
I have some other star shots some are good some are bad.. its usually me just practicing.. I have always just turned it all the way to the right, and picked the nearest thing to focus on and test shot till i had it in focus, as i turned the focus slightly back to the left.