alt Hacker News> Half-Life 2 sure won't play quake maps nor will it play hl1 maps.
Not without modifications but Half-Life: Source is essentially a tech demo to show that they can be ported easily (if you are OK with dropping some pesky features like randomized wall textures).
AFAIK hl1 maps needs to be open in hammer, tweaked a bit and then recompiled to function in hl2. You also better have those originals .rmfs rather than a .map or a even worse, a .bsp :)