That said, we love to help anyway, so here's some info for you to sift through:
For the front, just do the full FZR600 front end swap. That will get you a wider front wheel and a big brake improvement by upgrading to dual front discs.
FZR600 Front End Swap
There's a couple options for the rear wheel. The 1990-1998 FZR600R uses a half-inch wider (18" x 4.0") version of the same exact wheel. It's a direct swap, and will safely run about the widest tire you can fit in the stock swingarm: 150/60-18 (160 can be done, but it's dangerously close to the chain, and technically a bit too wide for a 4.0" rim.)
Clarifying the FZR600 Wheel Upgrade
Our brilliant leader and Chief Engineer, Radare, recently finalized the best option for the rear, though. This one gives you a wider wheel in a much more common size, giving you lots more tire options.
How-to: Install a 17" Rear Wheel (RF600 Rear Wheel)
If you do the front end swap, you'll likely use R6 front brake calipers, but not the wheels. R6 wheels won't work on an XJ without serious modifications. The wheel itself is just too wide to fit in the swingarm.
Casper's 1994 Yamaha XJ600