SentaiBrad said
BIOS are what make certain emulators work. As a fore warning too, do not post a link to them in the forums. They are 100% illegal to distribute (unless someone reverse engineered and open sourced some BIOS... which I don't think has happened.). Since you are new to them I just wanna point that out.
As for PS2, PCSX2, there should be a lot of BIOS for the system. There are Japanese, European and N. American BIOS based on the different regioned consoles. Some can be beneficial in some cases, but for the most part I've only ever used the latest American BIOS with a date of 2006. Unrar the pack of them in your BIOS folder under PCSX2. Go in to your plugin / bios setting menu and select a N. American BIOS. They should be labeled Japanese, Euro, N. American + a version number.
As for Dreamcast, the emulators are so wildly bad I've mostly avoided them for so long. It's why I bought my real Dreamcast. There might be BIOS for each region, but there might just be one you need out there. It depends if Sega ever developed regional BIOS. I don't think they did... Anyways, in the Dreamcast emulator settings you just select the BIOS similar to how you did in PCSX2 but it will look different obviously.
If you are using RetroArch, the BIOS to the systems will go in your System folder. Under path settings you will tell RA to look in your system folder so it knows where they are, or it will crash. The BIOS also need to be named something very specific. This has been covered on the forums a bunch before and I will be making videos for the LaunchBox YouTube channel regarding this in the future.
lol of course I would be trying to do something some what illegal. I just found the video on YouTube talking about setting up retroarch and that seems easy to use.
I have a question about where to place a bios when I do find one. You mention about putting it in my system folder. The way I have things set up is I have a C:\Games folder which has Steam installed in it. To make things easy for me to find I figure I would just use that folder for my Roms too. So where would I put the bios file then in that case?