Selling custom computers on eBay?

I want to sell custom built and made computers on eBay. I see that a lot of companies and people have it so a person can actually choose different parts and select different things from drop down menus or radio button groups.

I design web sites and I know xHTML and CSS. But I cant figure out how sellers on eBay make it so people can choose the parts?

Let me know if anyone can...

Selling custom computers on eBay?anti virus protection

This is done using php rather than html. It usually requires some form of database program like mysql as well.

The pages that you see displayed on these auctions are not simply html uploaded to Ebay, they are php scripts that reference resources hosted on their own servers so they can take advantage of powerful scripting languages like php, and mysql.