It looks to me that the way you have it, you will get a diamond sort of motion.
[edit]
try something more like
NPC Code:
playerx+=-(distfromcenter)*(somesortofpower)sin(anglefromcen ter);
playery+=(distfromcenter)*(somesortofpower)cos(ang lefromcenter); //this might be -= (see earlier comments)
this has to do with the derivatives of sin and cos.
[/edit]