I'm fairly sure both games were stand-alone expansion packs when originally released, but since this is almost a decade later and it's Steam we're talking about, I think it's safe to say that you can play them without Half-Life 1. Half-Life Source should be good anyways.
If you get Blue Shift, get half life with it. Then get the hd fixed pack and blue shift unlocked off of fileplanet. That HD pack is the original pack that wasn't actually ported over to steam. Blue shift unlocked converts blue shift to a mod form so you can use the hd pack with it and also fixes a few bugs. Trust me it's worth it.
"Please don't beat my random plumber boyfriend with your giant monkey arms of death!" "Hell no! I'm gonna throw barrels!" Mario's GF and DK
Having just played through both expansions, I can tell you that you may want to pick up a retail compilation pack in stores if they sell them. The downloadable versions of Opposing Force and Blue Shift have bugs and are completely missing the entire great Opposing Force soundtrack used in both games.
I do benefits for all religions. I'd hate to blow the hereafter on a technicality. - Bob Hope I'm right about everything, every time. 60% of the time.