So, you want to use all your sprites from the older version of Half-Life with Steam, no problem.

This tutorial is going to assume you know how to search your hard drive and copy files to folders as well.

First you have to find the folder that you will be saving the sprites in. For every user this folder is different since all of your game information is stored in a folder with your e-mail address you used when you registered for steam. The image below shows an e-mail address highlighted in yellow. Replace that with your e-mail address that is registered with Steam. Then continue to the valve folder and you can copy your sprites folder there. Some people may experience trouble with the missing file crosshair.spr. Just make a duplicate of crosshairs.spr and name it crosshair.spr. Once you do that, all of your custom sprites will work in steam. If you make a models folder in valve, you can put your custom models there also.

If you want to add custom models from your old setup, copy them from your old half life folder and
create a folder called models and put them in there with the same folder setup.