There is a really lot of things that contribute to bad steering, if the car has alot of miles you may just want to replace everything at once, to keep from having to get $80 alignments over and over again.
Consider getting:
Ball joints, outer tie rods, new or rebuilt rack (which usually comes with inner tie rods), new PS pump, and any hoses that look worn.
Keep in mind, if you only get a new pump or rack (one or the other) you must make sure 100% of the fluid is out of the part that you didn't replace, because the old bad fluid will contaminate the new new parts.
I know it gets expensive, so if you have to, save up or compile parts until you are ready.
None of it is all that labor intensive, so you should be able to handle it yourself.