don't buy a box.
No. You cannot "upgrade" HL2 packages. Somethings to know:
Retail:
-You are ALWAYS required to have the CD or DVD in your disk drive. This is a requirement Vivendi made VALVe implement.
-VALVe, also as a requirement from Vivendi, is banning accounts detected with "no-cd" cracks.
-The disks are protected with SecuROM V5, which not all drives are capable of reading.
-The games work in "offline" mode indefinately. This means with retail, you don't have to connect to STEAM to play.
-It can NOT be converted to a "steam purchased" cd key. (Vivendi, again)
Steam:
-You never have to have a CD in the drive.
-You can burn backups easily using STEAM's built in backup system
-You get a lot more for your money. (Back catalog, DoD:S, HL1:S, etc)
Buy the silver package. Its the best thing to do.
well, that's what i hear at least
gogo hearsay