If all you're looking at replacing (upgrading) is the actinics, I'd suggest a WH7 ballast.  I can help if you've got wiring questions.

I have a wh3 ballast to run my two 28w actnic pc's.  Starts right up everytime, very quiet, and low heat with the ballast.  It's an electronic ballast for flourescent lamps.  Was easy to wire in.  You could always just re-wire the canopy, you can buy everything you need at an electrical supply store, from shrink tubing to the wire it's self. 

p.s.  someday I'll actually learn to spell antinic right.

FLOURESCENT:
The Fulham ballasts (workhorse brand) are electronic flourescent ballasts.  They will drive either normal output (NO), high output or very high output (VHO) bulbs.  Actinic is just a "type" of bulb.  Actinic bulbs come in the VHO variety and the NO variety. 

VHO = more light, higher energy requirements (less efficient)
NO = less light, lower energy requirement (more efficient)

The cost of the bulbs are about the same.  Given the choice, most prefer vho.

METAL HALIDE:
Metal halide bulbs come in two varieties.  Probe start and pulse start.  These bulbs require different ballasts.  Here's the ballast designations:

                                  Probe                 Pulse
                                  start                   start
                            --------------------------------------
175 Watt                     M57                     M137 or M152
250 Watt                     M58                     M138 or M153
400 Watt                     M59                     M135 or M155

The difference is mainly in how the bulb is started.  Probe start is the mainstream MH system in the USA.  Pulse start is more popular in Europe.  The bulbs are not (under most circumstances) compatible with each other.  Pulse start ballast and bulb combination results in a longer bulb life, higher lumen output and better color retention when compared to probe start ballast/bulbs.

The Radium bulbs and all HQI double ended bulbs are pulse start.  Most other reef bulbs are probe start.  The Ushio is a probe start bulb.  The AB bulb is, I think, a pulse start bulb, although some people say it works fine in a probe start ballast.

[edit]  Most electronic MH ballasts will run either bulb.

Kevin,  are those 175 watt bulbs?  I've heard that about those.  I've got 250 watt Ushio 10K's with a probe start ballast without problems. 

The euro bulbs (Ushio, AB, other kockoffs) are a bit of mystery to me.  I think (this is IMO) they're actually pulse start bulbs, but they've incorporated a "probe" into the bulb for USA sale and it's hit and miss, especially with the euro knockoffs, on whether or not a probe start ballast will fire them.

I don't think it really matters.  Pick a type of bulb you want to run and buy a ballast to operate it.  Unless you want to spend the extra bucks on an electronic ballast.  They operate more efficiently and can usually fire either type of bulb without an drawbacks.

I bought a couple Advance 250 W ballasts and will mount them in an old computer case (gut everything out other then the fan and PS).  It looks fine sitting next to the stand and it has a built in fan that comes on when the lights come on to keep everything cool.  An old computer case can be had for almost next to nothing ($5 or so from the DI or free if you look hard enough).  But $150 for a dual 250W bare boned system is a very good price...

Don't post stupid questions until you know what your talking about like I just did.

Not your question, the one I wrote then erased because I didn't do my homework first.