We contacted a number of the bigger on-line poker sites on your behalf to see what the story was. The bad news is that none of them currently has a Macintosh version of their software; the good news, however, is that they do offer some solutions and confirm that they have players on their sites who are successfully playing with Macs. Here's the word, direct from the horses' mouths:
"At this time, we do not have any plans to develop a Mac version of the Paradise Poker software. However, several of our players are successfully playing with no problem at all by using a PC emulator. Our understanding is that both SoftWindows and VirtualPC work very well with our software."
"We are sorry to inform you at the current time our poker software is not compatible with Mac computers. We are currently developing a program that will be compatible with Mac systems, however. Please check back in the near future for the release of the Mac poker software. Should you require further assistance, please do not hesitate to contact us."
"We are very sorry, however we do not currently have a version of our software available for Apple Mac machines. Please be assured that we will certainly take future demand into consideration for the development of such software.
"In the interim, you may consider using a cross-platform application such as Virtual PC to run our software on your Mac machine. Virtual PC works by emulating a Premium-based Windows machine on your Mac. When you launch Virtual PC, the Windows Operating System appears inside a window on your Mac desktop. You can switch back and forth between your Mac OS and Windows as easily as switching between any two windows on your Mac desktop. When using Virtual PC, you can copy and paste text and graphics between Mac and Windows and drag files and folders from one operating system to the other."
As Virtual PC is commercial software, you will need to visit their website for further information:
apple.com/macosz/applications/virtualpc/index.html
microsoft.com/mac/products/virtualpc/virtualpc.aspx?pid=virtualpc
"We do not currently support Macs, but there are several players who successfully use Windows under Virtual PC emulation on Macintosh."
Note, however, that the install program itself will not work under Virtual PC and you will need to install first on a PC, and then copy the PokerStars folder to your Mac. The subsequent program updates do seem to work though.
Virtual PC has been acquired from Connectix by Microsoft and is now available from www.microsoft.com [see above link supplied by Empirepoker]
"We are sorry to inform you that we do not have an UltimateBet software version for Macintosh yet. We suggest you to use the Virtual PC program which lets you run Windows programs on a Mac [as above] or something similar - visit the following links: www.emulators.com or www.MacMAME.org, where you will find the latest emulators and updates for older emulators."