I would try selling your old stuff on craigslist first. If you get $40 for it, go for a 2x2gb of pc6400 in one of the following brands: corsair, crucial, kingston, pny, or hynix (samsung). I would not pay a premium for 1066 ram, unless you want to overclock.
Yes. You may also get lucky and find it on craigslist for less than retail. You can take your box with you to test it out if the seller permits. I've found the 2x2gb pc6400 kits as low as $50, but $60-65 is the average price used in the usa.