I have not used either, however:
1. The i3-330M should be faster than the T6600.
2. The i3-330M + chipset compared with the T6600 + chipset should draw less power and have longer battery life.
3. The Intel video of the i3 series is more capable than the corresponding Intel video of the mobile Core 2 Duo series. However, if the Dell laptop uses a fast Nvidia or ATI video chip then the capabilities of the Intel video won't matter.
4. The greater speed of the i3-350M compared with the i3-330M is probably too small to be perceived.
5. If I were buying a laptop I'd choose the i5-520 series because it has the AES-NI instructions in hardware for cryptographic processing. With this processor I could use Microsoft BitLocker full disk encryption for data security and the performance impact would be minimized. The i3 series doesn't have the AES-NI instruction set. Using full disk encryption makes access to the laptop data very difficult if the laptop is stolen.
1. Check the above information yourself.
2. I'm not an Intel or Microsoft employee.