You can download buttons off the web from various freebie sites. I think I heard Bill R mention that in another post. A simple googling of "web buttons" or something of that nature will most like give you tons of options.
I personally use Paint Shop Pro for my graphic work, but like any similar program, it takes time to become adept at it.
I tried using the DHTML Menu builder early on for the same reasons you are mentioning, but I ran into another issue of it moving around on the screen. Again, Bill R came to the rescue with a solution for that, but I prefered the look of the Flash Menu's. If you are familiar with any reasonably good graphics program, you can most likely take the buttons you like from the ones provided by CC, and stretch/grow them to the size you need.
Remember that Flash Menu builder creates two levels of menus. I'm, not totally sure how the menu decides on it's final size, but im sure it takes into account the sizes of the buttons on both levels. It might be safest to use buttons of the same size on each level, even if you dont use the second level.
Scott Tucker