What the average low-end user is using today is going to be pretty different from what the average low-end user would buy if they bought a new machine today.
Sorry, I thought he was planning to buy a new pc and answered accordingly. :)
An entry level pc is without a doubt a machine with an unexpensive main board and an integrated video card. Anything that requires a AGP or PCI-E video card automatically loses this share of the market.
Then, you have gamers with an average budget, which are the majority and use at their best video cards in the range of the ones shown in my post above (usually slightly cheaper).
Valve ran such a survey regarding their userbase, which could be considered the perfect reference for this situation:
http://www.steampowered.com/status/survey.html