Was looking on Lenovo's site for a similarly equipped laptop as the Dell. Kept both stock, upgraded the processors both to dual core 2ghz, graphics to Nvidia 256mb discreet, both with Vista Home Premium. Lenovo was around $70 less, if that means anything to you.
Dell and Lenovo are both great, and I do happen to have a newer model Lenovo, and an older Dell right next to me..Both have stood up to some abuse, and either would be a good choice. I'm a bit partial toward the Lenovo, but I suppose it's up to you to decide which fits your needs best.
Hopefully this link works for the 'Lenovo ThinkPad SL500 15.4" wide screen with discrete graphics' (I custimized the link that Shane posted, ended up being 999 when I finished. Unfortunately I'm unable to share the results as apparently you can't show others what's in your cart... Ending prices were $999 for the Dell, $924 for the Lenovo. )
EDIT - That link doesn't show how I customized the Lenovo. Essentially I upgraded the RAM to 2gb, upgraded the screen (I think), downgraded from Vista Business (just to have the same OS as the Dell. I've got business, and for the extra $30, I'd stick with it. I just downgraded for comparison, as the jump up $150 on the Dell to Business seemed a bit much), added a finger print reader and a built in camera. (Found the custimization screen.
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For the Dell, Everything was the same. Had to upgrade the RAM, processor, graphics card, etc.