In short, the Intel Core 2 Duo is based on a new processor architecture that is designated to replace the entire Pentium line, including the Pentium 4 and dual-core Pentium D. When they debuted, even the low-end Core 2 Duo E6400 bested AMD's creme-of-the-crop, and continues to be one of the best performers on the market. If you are looking for power, the Core 2 Duo is the place to look. On the other hand, you can purchase Pentium Ds for a decreasing cost as they are slowly phased out. For you it doesn't really matter which you get, so if you're on a budget look to the Pentium D line. Otherwise, the Core 2 Duo is your best bet.
As to the manufacturer, Acer is a serious contender in the laptop market, but for a desktop I would prefer a Dell given the price and level of support they offer compared to Acer.
Hope this helps,
I'm getting a new Desktop PC after having sold off my 2 and a half years Acer Intel Celeron D Desktop PC. I'm thinking of getting either a Pentium D PC or the latest Core 2 Duo. I understand both Procesors are pretty fast but not sure, in particular the big differences between the 2. Other than using the PC for surfing the Internet and Emailing, I also play some PC CD games, not the sophisticated and resource demanding ones though, watch/download movies and music too. Which one should I settle for? Also, I've decided either on Acer or Dell. Which one would you recommend?