1. Pentium Ms are centrino processors. However, depending on the centrino processor you get, your performance will vary widely. For example, I use the sonoma chipset which is equivalent to or faster thn Pentium 4 3.2ghz processors w/ht. The main differences are: less heat and much “thinner” (portable).
I haven’t used AMD processors, therefore I cannot comment on them.
2. Yes, 1GB should be fine for MOST tasks.
3. After Effects is a memory hungry app. The more RAM you feed your system, it will happily utilize it. But, if you plan on doing a lot AE work alongside Premiere Pro and Photoshop, I would reccomend upgrading your memory to 2gb.
Aanarav Sareen
Adobe Certified Expert, Premiere Pro
https://www.asvideoproductions.com/video