There are a couple of options that didn't come up on the discussion you started on 8052.COM regarding your occasional need for a digital waveform that's precisely timed, or constrained in some other way. If you want to handle this from within Windows, which is often a very convenient option, I'd suggest you consider one of the various ALTERA or XILINX CPLD or FPGA boards as a vehicle.

For example, if the need is to generate a waveform of a precise shape, and simply recirculate it in a shift register of arbitrary length, you simply need a RAM, a counter, and a shift register output. I do this sort of thing quite often, and have found that a basic sort of "video refresh" circuit, i.e. counters for timing and memory for waveform storage, along with a PISO shift register for the final output (and perhaps a logic-level mosfet as an open drain level shifter), together with some control logic, is quite satisfactory. It's a bit of an effort to generate the basic skeleton, but it's easier than a real raster-scan video circuit because you don't have the sync and blanking controls to contend with and because you have complete control over the memory content and timing. With these JTAG-programmable boards, a single board can provide quite a wide range of functions.

All it requires is an oscillator of a frequency suitable for generating the finest resolution that you require and a synchronous counter capable of cycling through the memory. Your SPARTAN-3E EVB might actually have all the resources on it that you need, aside from the level-shifter. I prefer boards with a prototype area so I can put level shifters, etc right there where I need 'em, but you're not constrained in that way. Of course you could buy their prototype board. Those come with or without the solderless breadboard, and they're actually designed primarily for that breadboard, in that the interconnection sockets located on the component side really have to be removed in order to allow for proper prototyping with wire-wrap, which is done on the opposite side of the board. That proto board without the solderless breadboard is not expensive, and I suspect you will find it quite useful. Using the DCM, you can probably multiply up whatever crystal you choose to a useful frequency, and if you send off for a sample of a fast DAC, and a decent buffer amplifier, you can even generate arbitrary analog waveforms with it.

What's really convenient is that you can program up the circuit and simulate it before going to any further bother. That way you don't have to build something first, just to find it really doesn't meet your needs.