It's pretty easy to pick up, certainly much easier than modelling; in fact this would probably be a good learning exercise since all the geometry and entities are already done.
For a simple convert all you do is open up Source Tools > Hammer (needs to be the source version)
Once you've got Hammer open you want to convert the HOE wad textures to VMT format - which Hammer will do for you, just click on the "WAD to VMT" in the File menu.
In the maps look for any textures which begin with ! (eg !Water) these textures all need to be replaced with Source Liquids - which is easy to do with the Replace Textures function (Tools > Replace Textures)
Then just open up the HOE map files and export them to VMF.
Compile the maps using TCG Compiler
Useful tips / tutorials can be found on these pages
http://developer.valvesoftware.com/wiki/Source_Mapping_for_Half-Life_1_Mappers (a good reference point for mapping in Source)
http://developer.valvesoftware.com/wiki/Porting_Goldsource_content_to_Source (models, ragdolls)
http://developer.valvesoftware.com/wiki/HDR_Lighting_BasicsEntities might need changing, depending on which Source game you port to
This is just the bare minimum you need to do in order to port to Source, doing other stuff like inserting Props and higher res textures is pretty easy to do.