As for the laptop lasting 5-6 years…well, good luck!Â
I dunno about that, I’ve been working on some Pentium MMX laptops lately that run pretty beautifully with a custom installation of Slackware Linux. If it weren’t for their awful resolution and the fact that the 16MB of RAM gets a little choked when dealing with Java intensive web-apps, I would probably use one just for the web.
As for your system, switch, no one deserves a celeron for a desktop. Since you don’t need top of the line I’d recommend a Sempron or a single core Athlon (with the recent price slash they are quite nice and the Athlons are better than any P4). Dual core if you’re willing to spend more than $150 on the processor alone. As for video cards, ATI Radeon x1600’s should be able to do just about anything you demand of them, or maybe Nvidia 7600s as they should be comperable in price and performance.
Other than that, if you’re building it yourself get a dependable power supply. No sense risking your shiny new components with a psu that has the potential of frying them. I trust Enermax, Antec, and Thermaltake mostly, but there are others that build quility components.