I 2nd the Dell laptop choice, and moved exclusively to a Dell Inspiration 8000 laptop when I bought SolidWorks 2000 years back. It still functions well, though it is merely a backup in case disaster ocurrs at this point. Unless some power issue comes up with massive assemblies, I don't see a need to leave the m60-m70 laptop for a desktop. If you like to do a lease-purchase, Dell will sell you a brand new spankin' M90 for a few hundred clams a month.
Since then I've upgraded to the Dell M60, 1.7 ghz, and have maxed the memory and a fast hard drive, and it is now 2+ years old and still a work horse that I can move around reliably. I have a friend doing medical hardware design, who still works efficiently on his M50 at his home office and the company he does most of his work for, and their vendors.
I just do not let the M70 on the Internet, except for critical updates from Microsoft, if I really think I need them. This issue is just me, though, as most people set up adequate firwalls and anti-malware programs. Those programs can slow down SolidWorks, though.
I personally let my MacBook Pro do all my Internet work (& incendentally use it for SolidWorks on the road now, too, as they've finally made the move to the Intel CPU).