first of all NO there are no PS2 emulators but there are PS1 emulators.
the main reason why there are no PS2 emulators is because sony started encrypting there discs so no-body could copy them. pc's could not read the disc so how could they burn them.
after some googling i have found that this encryption is now failing. hackers have found the right code so in a month or 2 we can copy these discs and in 8 months PS3 is in stores so sony has won.
the main reason why PS2 emulators also not work is because of the massive CPU/GPU power needed. PS2 games speak directly to the hardware, no OS is between. with the PC windows handles this because PC can have many different types of hardware(e.g a ATI or NVIDIA card?) this is done by software like directX(direct3d actualy). so the emulator has to cover this to. for every frame it produces it has to emulate it to something readable by direct3d and there go our frames, thus framedrop. also a problem is that PS2 is 128-bit while pc's are 32-bit maybe the AMD Opteron does correct this a bit since it makes this gap some smaller(instead of 4 times bit-emulation only 2 is needed) but still the diffrences are huge.
so even if there whas some perfectly crafted PS2 emulator it would as notices before need between 5 and 7 GHZ and about 2GIG ram. just to cover the delay between al those layers but there is hope.
an AMD athlos at 2Ghz is equal to a Pentium 4 at 3 GHZ and and AMD Opteron at 1.4 Ghz is equal to an Athlon at 2Ghz so an Dual AMD Opteron 2x 2.2 Ghz = 4.4Ghz is equal to and athlon at 6,28Ghz wich might be just enough to use an PS2 emulator that support Dual proccessor and runs at 64-bit ofcours. so if someone has some money and can program such a program he or she might be playing PS2 games wich will be obsolete in 8 month from now. so have fun.
conclusion: there are no PS2 emulators because its just not possible to create one.