||I haven't seen any free VBx scripts to do this, but there are a couple of commercial parcel editing products from LandWorks.com and Tobin.com.
It wouldn't be too difficult to write a script that did a straight bisection, but the problem is when you have non-standard sized sections - for example if the section is only 600 acres instead of 640. The BLM et. al. have various rules for how you're supposed to quarter these irregular sections, which can be different in different parts of the country, so you'd need to look those up - if you're concerned about extreme accuracy. The commercial tools also *should* take these rules into account.