If you're on a budget and want a Windows XP system, I recommend a Dell system.
PC-wise, good specs for productivity to expect from lappies nowadays:
- A dual-core processor. Intel is the primary player in the mobile market for this right now and their Yonah 'Intel Core' processors are great. The base model is the Intel Core Duo T2300 (1.66GHz). They are also very power efficient, so expect battery life of upto 5 hours or so for general productivity usage. Intel Core processors are also generally combined to their 'Centrino Duo' platform, which also includes wireless connectivity for the b(11Mbps) and g(54Mbps) protocols.
- 1GB of RAM. Although many vendors still offer 512MB, I would strongly recommend 1GB and even 2GB if you intend to upgrade to Microsoft's upcoming Windows Vista.
All other specs are really up to you; if you want alot of secondary storage, consider a bigger hard disk. Nowadays standard hard disks for lappies come in the form of 40GB (entry-level laptop), 60GB (mid), 80GB (mid-high), 100GB (high-end) or 120GB (top-end). 120GBs are usually only an option for 17" notebooks with the standard being 60GB/80GB for 14" and 15.4" ones. Speaking of screen sizes, remember that a 14" and 15.4" widescreen have the same resolution screens (WXGA+), so even though a 14" screen is physically smaller, you're not missing out on any extra desktop space. For that reason many prefer 14" if they want light. Get a proper video card for your laptop if you intend to upgrade to Vista (you've already mentioned that you don't play games, so otherwise I see no reason to fork out extra on a higher-end video card).
So right now you can grab a Core Duo T2300, 1GB, 80GB system from Dell for about $1,350. Get a 9-cell battery if you want better battery life and the 15.4" WSXGA+ screen upgrade if you want to run your computer @ 1680x1050 resolution.
If you're more familiar with Mac operating systems, then consider the new Intel processor based MacBooks.