Weight Guidance... help.

So I purchased the following motors and wheel caster (links below). and planning to use a lightweight sheet of wood for chassis.

How can I know whats the appropriate weight the motors can hold/run, like will they be able to hold a 7 pound laptop? What is the range of weight they can hold? how do I calculate it. Thank you

Motor Ratings (at 7.2 VDC): No-load Current: 0.27 A @ 310 RPM Stall Current: 4.8 A Max Torque: 4.6 lb-inch (5.3 kg-cm)

Does it mean I can't go over 4.6lb?

http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/587/Default.aspx?txtSearch=motor+wheel+kit http://www.parallax.com/StoreSearchResults/tabid/768/List/0/SortField/4/ProductID/527/Default.aspx?txtSearch=ball+caster

It's difficult to say. Each motor will have very roughly one pound force of tractive effort. To decide whether that's enough to move your 'bot you will have to work out whether that will exceed the rolling resistance (at your target weight) and the effects of the slope. If you're dealing with a 'bot that only weighs a few pounds and only needs to move on smooth level ground (or nearly level ground) then a set of four of these motors seems ample to me. If you want it to drive up the side of a mountain, that might be asking too much of them.