Short answer: No.
Long answer: No.
You're pretty much SOL. Nothing to emulate or virtualize a x86 on PowerPC to a decent speed. Upgrading to an Intel Mac would be your best bet, then you have several options such as VMware/Parallels (Virtualization), WINE ("Emulation" / Compatibility Layer), or simply running Windows XP/Vista/7 natively (BootCamp).