DC/DC Conveter
There are modules that you can use for this simple DC voltage conversion... Try to search for different DC/DC IC regulator manufacturers because they might give the module to you for free for you to evaluate their IC regulator if you are a potential bulk buyer... I'm actually evaluating an Enpirion DC/DC IC regulator, and we had their module for free, that's by the help of our Purchasing Dept...
But if you aren't capable to have it for free you might want to build it on your own. Try to use the Power Supply Circuit Builder of National Semiconductor, it is available in their website.
regards,
ζεΦ
Added after 7 minutes:
Btw, use a switching regulator for converting 24V to 5V because this can give you the most efficient conversion esp if you will drive a current that is greater than 1A... If you will use a Linear for this one, huh! better to prepare for a big heat sink and fan because that will generate a lot of heat...