D600 are ok laptops, although chances are its 1024x768 max res. You can upgrade the RAM in it (two slots, max 2x1GB) but its DDR so its also expensive (~£40 per 1GB, new). As a simple email/web machine it will do ok.
Depends if they have been used on desks or if they have been carted around in a bag. Ie, if the screen has big white compression marks etc.