Well, I was cruising along and saw this post so i decided to present you with some of the options for doing this..
You can get a sony vga adapter, available as part of the linux kit which has been on the market for several years, note this is only compatable with the PS2, meaning the larger version with the accessory bay in the bottom, as opposed to the PStwo which is the slim design currently available.
Compatible with either model you can get a vga upscan convertor which will plug into your ps2 and allow you to use the monitor for either the ps2 or your computer, at the flip of a switch. some of them require special drivers(a disc you boot the ps2 with that enables the adapter, then prompts for you to insert your ps2 game to continue) while other models rely on the component output. typical price range last time I looked was from $20 up to $100, I would recommend spending around 50-75 because for this type of device I have found you get what you pay for...
as a last resort you can run the signal into your tv tuner card, preferably using the s-video signal. however it by far will be the worst of your options...
as for the audio, most of the upscan converters will have a stereo audio out jack that you can run to your sound cards line-in, or personally i use the optical connection, which tends to be much cleaner sound...
hope this helps get you started, feel free to ask me any questions and i'll answer them as i have time.