A mini-ITX system might be just what you need
In case your not familiar with these I'll explain a little, the ITX form factor was developed by VIA for ultra small PC's using integrated motherboards. As well as the usuall video, sound, etc they also have the processor integrated, being a VIA solution these are currently their C3 processors. The benefit of the C3 are they have low power cosumption which in turn means low heat which is necessary as the cases don't tend to have much room for cooling. The C3 processor isn't as powerful as the Intel and AMD equivelents but sufficiant for the type of appications these PC's are used for which is normally as part of an AV system for playing back DVD's, SVCD's etc.
Judging by what your using the PC for it would be much faster than the 486 your currently using but not over the top like a P4 or Athlon XP would be.
For more info on these systems as well as prices for the parts pop over to this site :-
http://www.mini-itx.com
As far as programming is concerned have a look at Borland Delphi, it should allow you to do what you want without the steep learning curve of something like C++.