Hey Pager,
If there is a rental place near you they should have them, though you might need help loading and unloading it ( they are HEAVY and in my opinion the heavier the better. ) while I agree that your location dictates when you should do this, nearly any landscape pro or web site will tell you spring AND fall are the opportune windows for ( core ) aeration and in the summer, if you fell the need, use dagger ( straight blades without the hollow core ), this prevents your soil from drying out. If you decide to aerate or have someone do it, remember the more passes you make or different directions you do it from, the better. If it looks like the tenth annual cats#*t competition was held in your yard, then you did it right!
When you core cultivate, you're also leveling your grass area and filling in low spots, so don't rake up the 'mess' left behind.
I would also suggest that you put down some grass seed immediately after. Just be careful where you get your seed, if you read the back of the package, most will have anywhere between 2-12% weed seeds. That doesn't seem like much until you realize that for every 100 seeds you use 2- 12 will be weeds!
Finally my last bit of advice (thank goodness, huh?), Don't fertilize until the grass has been cut twice, this will keep fertilizer burn to a minimum.
