The video card will be more of the issue... and if you want windows support
ArcadeVGA is the easy way.  
Trident64 can do it also with hacked drivers.  (one other I think)
Other then that.. your dealing with making sure that you don't turn on the monitor until AFTER your INSIDE mame/frontend or you might blow up the monitor.  AdvancedMame and AdvanceMenu is what you would want to look into.
I don't know why everyone makes the video card out to be such an issue.  Actually the video card is an easy part.  Many of them will output a 15KHz signal, and then again, many will not.
S3 cards don't, ATI cards do.  nVidia do, a lot of Trident cards do.  I've got an STB Velocity that does it flawlessly.
If you're getting a J-PAC, don't waste your money on an ArcadeVGA.  The J-PAC will automatically knock the signal to an acceptable level before they are knocked down via drivers.
Windows @ 15KHz, OTOH, 
is an issue.  For this, the ArcadeVGA will work well. 
What other methods, besides the ArcadeVGA, work for getting Windows @ 15KHz?