| The guy at Dell is partially blowing smoke. Another reason not to buy Dell. The fact of the matter is that most current Pentium 4s have Hyper Threading (HT) technology. HT means that your software can be programmed (by the programmers, not the user) to view the processor as dual processors. Essentially this means that the processor can be doing double the work at the same time. HT will speed up most tasks, but if the software is designed for it, there can be significant increases.
So both processors are hyper threading. A Mobile processor's clock speed is generally lower then a desktop's. That does not mean it's slower. Clock speed is not the only indication of performance. Generally you can about double a mobile processor's clock speed to compare it wioth a non-mobile processor. So the guy wasn't lying when he said it would preform like 4Ghz. He was just giving you a BS story about why. Basically, it sounds like the guy was trying to explain the clock speed difference to you in a way he thought you would understand. But in doing so he gave you wrong info.
The advantage of a processor specifically designed for mobile use is longer battery life, generally 50-100% better and a cooler running machine.
However, I prefer and highly recommend the AMD Athlon 64 processors. Right now the Athlon 64 is the only true 64 bit processor available to consumers. This means that when the new Windows Vista (I hate that name) comes out next year an Athlon 64 will be able to take full advantage of its 64 bit features. Also the Athlon 64 is the only processor with hardware anti-virus protection. When I needed to replace my desktop at the end of last year, I only looked at Athlon 64 based machines.
As for the video cards. Unless you plan on using the machine for heavy gaming it shouldn't matter much. Both are good video adapters.
Dell's service has been getting poor reviews lately. I think you will find, when you compare, that HP laptops are extremely price competitive with Dell once you compare the full configuration and include all the costs (like shipping).
Try tomshardware.com for comparisons. | 
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