I don't know what HL-online is, but I'll assume its an internet playable game... The other guys had points about the Winmodem and video card. Winmodems are taxing, and you are hard pressed for CPU slices... Let's face it, you hardware is at least 3 years old, and maybe 5 years old. If the game is current, you're lucky it will play at all... I don't mean to sound crass but the software developers forget sometimes that we're not all able to use current technology. The days when a programmer took extreme pride in their ability to perform big tasks with small hardware are gone... 4k graphic demonstrations that would fit in the boot sector of a 720kb floppy disk are a thing of the past. Programmers have access to simply fabulous hardware as developing platforms. I digress...
Do you have AGP? If so the best bang for buck is by far the 32MB NVIDIA TNT2 MX from Cardepert (Gainward). PC magazine agrees, and I have had opportunity to test some of the best hardware out there, its part of my job. Its not the fastest, but for $120US you cannot even come close with most of the others. I'd say its 75% as fast as the $500 cards I have tested.
If yopu have PCI only than I guess you should look for any TNT2 or TNT (both NVIDIA chipsets).
A RAM drive is going to be a pain for you, and just how are you going to install that game into what little RAM you have available? I don't think that's worth the effort. If it will fit (must be small)there used to be DOS commands to creat one. I just checked my system but can't find anything, so I guess just search the Web for a shareware tool or something.
Really.... If you can do it, upgrade. If you can't, ditch the Winmodem, and get a video card.
Hope this helps,
James Heal