If you're happy with Quake on a 100 MHz Pentium, you should be happy with Half-Life on a 120 or 133. Or will the software version be ab. The software version does everything the hardware version does. Colored lighting is in the software version. The fogging that Jay Stelly has done for our water effect is pretty amazing, especially when you see an Icthyosaur zipping out of the depths.
Transparency works just fine in software.
Decals work fine in software. Additive transparency for fire works in software. Most of the people at Valve develop and play Half-Life in without hardware acceleration. We've spent a huge amount of development time making sure the software version is cool. We love hardware, but the bulk of people who buy Half-Life won't have a 3D accelerator.