Drilling in to lintels can be a bad idea. At some point you could hit steel and it then can be very tedious. Accuracy can go out the window ( no pun intended ) and you end up with a mess. What I find is always a very good idea is attach a good piece of wood to your poopy holes then attach the fitting to the wood. The wood needs to be the same length as your curtain, blind or whatever and about 50x20mm. The advantage of this is that once you have the wood fitted, not only is it easy to hang your blind or whatever, but its easy to fit a new blind or curtain rail in the future. I just paint them the same colour as the wall.
And don't worry, lintels really are a pain. I have done this for years and years and yet can still end up with a hole big enough to fit your head in. Once the wood is in place though you need never do it again.