>>Another option is to use touch screens, which are fairly inexpensive and in general give users faster 'point and click' operation than a mouse. No extra programming is necessary. Most of our fast paced retail customers are using touch screens. They love them.
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>We prefer touch screens too. But some of customers prefer the use classical desktop PC's or some of customers has old POS terminals which are don't support touch screen...
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>That's our POS main screen:
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>http://img504.imageshack.us/my.php?image=tposzi7.jpg

That is a nice, clean, touch screen friendly design. Retail Management System is similar. It also provides a pop-up onscreen keyboard in case your user doesn't want to have space for one (it's not used much).

Old, non GUI designs usually have the advantage of being very fast on reasonable hardware. They just need to be designed well witht eh user in mind.