Hey there.
I have a first gen Macbook pro. 1.8Ghz core duo and I upped the ram to the maximum 2 Gigabytes. It's also a 5200 rpm 80Gb hard drive as standard.
I use After Effects 7 regularly and have done many special effects on my laptop for film and music videos and it handles it fine.
I work with Quicktime movie files and have used targa sequences now and again and have never swore at my computer once! This is of course coming from a G4 laptop, so I had gotten used to slow previews and renders so this thing seemed to fly when i first used it for effects.
The only thing to remember for preview renders in After Effects is that it's more a case of how much RAM you have for it to build the preview to. For example, if you had just 1 Gb ram you might only get a 15 second preview (depending on the setup of the comp) and more ram equals more preview!
I have 2Gb of ram same as your setup and I can get about 10 seconds preview on a HD project with everything turned up full, so if you can max yours up to 4Gb ram, then you should get about double that. It also depends if you have other programs open in the background or not which use ram.
Obviously, when you render, the ram is generally insignificant, unless you are on 512Mb or something, and I find mine can render a 10 layer no lights or 3D camera angle HD scene about 10 seconds long in about 5 minutes, so yours should be quicker.
As for Shake, I tried it last year when a project came in where I had to do a lot of four corner pin tracking in HD, and knowing After Effects amusing way of NOT actually following the tracking points, I turned to Shake.
I still wish i knew someone who could sit down and show me how to do the stuff I do in After Effects but in Shake as I loved it! It seems to be non destructive when rendering. I don't know if that is phrased right, but what I mean is that it flew! previews and rendering were severely quick! well, compared to After Effects they were!.
I personally see no problem running AE or shake on your laptop as mine runs like a banshee on rollerskates!
Mel