Jon-H,
  I have replaced the bearings on my XJ40 in both the front and the rear
and it is an easy job.  Well, it is as easy as any other car.
You do not need a press.  Like any other set of bearings, you can drive the
race out with a drift.  Or in my case, I used a large flat-head screwdriver.
You need to take a bit of care not to score the hub as it is aluminum, but
it is any easy operation.
I suggest you buy the kit that includes the inner as well as out bearings
and races as well as the oil seal and a bit of bearing grease. There have
been situations where the suppliers have shipped incorrect oil seals when
you buy the parts separately.
Use the driver to pop the old race out.  Use the OLD race and a block of
wood to drive the new race in. That way no damage is done  to the new race
or the hub.

The front bearings are easy and self explanatory.  You MUST make note in the
rear as to how the assembly comes apart in order for it all to go back
together properly.  There are washers and spacers inside the hub.

One note:  You will be confused at first as to how to get the hub apart. On
the inner side of the hub, you will see a toothed gear. (on both sides if it
is an '87,'88 or '89 XJ40). This "gear" is for the ABS sensor.  If you look
closely, you will see the toothed gear is a force fit onto the stub. If you
take a 24MM (I believe) socket, it will fit perfectly inside the toothed
gear and rest on the rim of the stub. With the assembly raised, you can hit
the socket with a hammer and the whole stub should drop out of the toothed
gear thus making everything accessible.

I have pictures and diagrams if you are interested.

Cheers
Webserve