Take a look at Kev’s neat tutorials. Especially this one:
http://grexengine.com/sections/externalgames/articles/Kevin%20Glass-Space%20Invaders%20101-2.html
He also explains the differences between the timers n stuff. Well, take a look 
Take a look at Kev’s neat tutorials. Especially this one:
http://grexengine.com/sections/externalgames/articles/Kevin%20Glass-Space%20Invaders%20101-2.html
He also explains the differences between the timers n stuff. Well, take a look