Sounds to me like you just want a macbook. My lowest-end first-revision macbook was smokin-fast and easy to take everywhere. After adding more RAM, I was using it for numeric computation in MATLAB running on Linux virtualized under Parallels and I could still web-browse etc. with the other core. I didn't expect it to be able to handle the brutal amount of abuse I gave it, but it was happy. I miss my macbook 🙁
If you're not playing games then a normal Macbook will be fine for what you need it for. If you want to use a lot of programs at once, consider getting 1 GB RAM instead of 512 MB. That's my opinion...
My friend has a MBP 1.87Ghz, 2GB or RAM and I'm using a MP 2.00Ghz 512RAM. We both use our beloved notebooks to produce, master and perform electronic music. The programs we use are very intensive and honestly speaking, there is not much difference between the two in terms of raw power. The MacBooks certainly hold their own and are indeed quick little notebooks. For just basic functions a Macbook Core2Duo with a gigabite of RAM would more than suffice.