  Recent discussion of the effects of finite source size on high magnification
microlensing events due to MACHOs motivates a study into the feasibility of
observing such effects and extracting the source radius. Simulated observations
are generated by adding Gaussian error to points sampled on theoretical
microlensing light curves for a limb darkened, extended source. These simulated
data sets are fitted in an attempt to see how well the fits extract the radius
of the source. The source size can be fitted with reasonable accuracy only if
the impact parameter of the event, $p$, is less than the stellar radius,
$R_{\star}$. It is possible to distinguish ``crossing'' events, ones where
$p<R_{\star}$, from ``non--crossing'' events if the light curve is well sampled
around the peak and photometric error is small --- i.e.~$\geq 3$ observations
while the lens transits the disk of the source, and $\sigma_{phot}<0.08\;{\rm
mag}$. These requirements are just within the reach of current observational
programs; the use of an early-warning system and multiple observing sites
should increase the likelihood that $R_{\star}$ can be fitted. The programs
used to simulate and fit data can be obtained via anonymous {\tt ftp}.

Astrophysics