If you don't plan on overclocking Tbred B XP1700+ just drops right in, even with your KT133A mobo. I have one working in an Epox 8KTA3PRO, myself.
If you do want to do a little overclocking it's still easy. My mobo can go to 150 Mhz FSB which means I can run the XP1700+ at 12.5 x 150 = 1875 without any mods. In my case, I need to increase core voltage a little, to about 1.70 volt. A7V133-C should yield similar results. (I'm assuming you have multiplier and FSB adjustmensts on that mobo).
Going to higher speeds gets a little trickier. Since these legacy boards don't officially support multipliers above 12.5x you have to play some tricks.
On legacy boards, CPUs with multipliers 13x or higher have their multipliers remapped. That is, you select something in BIOS (or by jumpers) and you get something else. Heres a partial list.
7x --> 15x
7.5x --> 22.5x
8x --> 16x
8.5x --> 16.5x
9x -->17x
You can also get 18x, 19x, 20x, and 23x.
See what I mean by tricks?
As I said, to get access to these higher multipliers your CPU has to have a default multiplier of 13x or higher. This can be because you have a genuine XP2100+ or higher. This can also be because you have mod'd your CPU (like XP1700+) or mobo.
Sounds reasonably simple but it gets more complicated. Most legacy boards allow these remappings as long as FSB is set at 100 Mhz but often have problems when FSB is increased to 133 Mhz.
My mod'd XP1700+ will boot at 15 x 133 with default voltage (1.6 volt). Some processors won't. 13x-14x doesn't work because of boot timing issues. 16x doesn't work because 16 x 133 is too much of an overclock (for my CPU) with default voltage. Some mobo establish their own default multiplier which add to the problems.
For example, legacy Abit boards sometimes try to POST at 20 x 133. 2666 Mhz is much too much of an overclock so it fails. Other times an identical board will POST at 20 x 100 but won't allow the switch to 133 Mhz FSB. A third board might work fine.
Even if there are problems there are workarounds for the legacy boards but they involve chip or mobo mods.
As for you A7V133-C. I haven't seen too much on legacy Asus boards (don't own one so I don't really follow that information). However, I'm positve an XP1700+ will work stock and that you can overclock as I described above. I just don't know what issues you run into if you attempt to access the higher multipliers but I'm also positive there are workarounds for the issues that do come up.
Sorry for the long post.
<b>99% is great, unless you are talking about system stability</b>