First, thank you for this site!
I will be attempting 3/4" oak installation. No expierence, no skills (not sure what I'm thinking).
This will be in my kitchen which has post in all corners and this portion of my house is over 200yrs old. The joists are very rough hand hune. On top of that is an old hardwood and then a layer of 1/4" plywood (I think). For the most part the floor is pretty level, considering. There are some dips here and there, deep enough that need attention.
Anyways, I dont want to put alot of extra weight on the floor and am wondering the best way to fix the dips. An uncle suggested plaster of paris. As far as shingles and shims, not sure how to go about it.

Forget your uncle's idea. Plaster is for walls and ceilings. Low spots in wood subfloors can be furred up by using layers of #30 lb. roofing felt or 3 tab asphalt asphalt shingles. You can use thin plywood as well. For starters, read this:
http://www.hardwoodinstaller.com/hardwo ... renail.htm

Thanks Gary! Are you talking about the roofing shingles that I have left over from my roof? I have alot of that.

Yes, CC, asphalt roofing shingles. That's what I meant to type but I guess it didn't come out that way.