I use a screwdriver kit like this one on ebay: http://www.ebay.com/itm/New-15-in-1-Scr ... 2c6760512c
It's only four bucks and works for 95% of my thinkpad screws.
On the rare occasion a torx screwdriver is required, this would probably work: http://www.ebay.com/itm/16-in-1-Torx-Sc ... 1c0bec8d46
But your ram cover shouldn't require a torx -- the first kit I listed will most likely have the screwdriver you need.
QFoam is exactly right -- those little screws are VERY easy to strip, and then you are struck with a project of removing the stripped screw and finding the correct size replacement -- so resist the temptation to keep trying to loosen the screw without the correct fitting screw driver --
If you don't want to wait for an online purchase, your local hobby store should have the same screwdriver kits.