I know the Compaq dv6000 (at least several of them can, I don't know about the oldest... you have not given us a model number you have given us a family/size which encompasses several quite different (internally) models), can use up to 2GB per slot, but I don't know about the Acer.
DDR2 memory is backwards compatible, go ahead and get pc2-5300 or -6400 for both, whichever you find the best deal on, and get some rated for 1.8V not higher since the laptops probably don't have an option to raise the memory voltage. Beyond that, you can literally pick whatever you want yourself (including whether there's a rebate) from Newegg or elsewhere. Recently Fry's has had some good deals on Crucial memory too, a few weeks ago I got 2 x 2GB PC2-5300 for $15 after a rebate. You should be able to find something with 1.8V and CAS5 instead of 6 at a good price.
Newegg had a deal recently for the following Crucial memory, $15 delivered w/o a rebate but they sold out.
http://www.newegg.com/Product/...x?Item=N82E16820148086
A week ago Newegg had these for $9 delivered:
http://www.newegg.com/Product/...x?Item=N82E16820134546
Either the memory market's price increases in the last few weeks have tricked down to retail products, or this is only a temporary rise and you'd save some money waiting till the next time a deal for what you need comes along. My crystal ball is broken but you might also check the Hot Deals forum to see who has the best deal at the moment if you don't want to pay a few bucks more at Newegg right now.
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