  We have used the WSRT to carry out an unbiased wide-field survey of HI
emission features, achieving an RMS sensitivity of about 18 mJy/Beam at a
velocity resolution of 17 km/s over 1800 deg^2. In this paper we present our HI
detections at negative velocities which could be distinguished from the
Galactic foreground. Fully 29% of the entire survey area has high velocity HI
emission with N_HI exceeding our 3 sigma limit of about 1.5x10^17cm^-2 over 30
km/s. A faint population of discrete HVCs is detected in the immediate vicinity
of M31 which spans a large fraction of the M31 rotation velocity. This class of
features is confined to about 12 deg (160 kpc) projected radius of M31 and
appears to be physically associated. We detect a diffuse northern extension of
the Magellanic Stream (MS) from at least Dec=+20 to +40 deg., which then loops
back toward the south. Recent numerical simulations had predicted just such an
MS extension corresponding to the apo-galacticon portion of the LMC/SMC orbit
at a distance of 125 kpc. A faint bridge of HI emission appears to join the
systemic velocities of M31 with that of M33 and continues beyond M31 to the
north-west. This may be the first detection of HI associated with the warm-hot
intergalactic medium (WHIM). The distribution of peculiar velocity HI
associated with M31 can be described by a projected exponential of 25 kpc
scale-length and 5x10^17cm^-2 peak column density. We present the distribution
function of N_HI in the extended M31 environment, which agrees well with the
low red-shift QSO absorption line data over the range log(N_HI)=17.2 to 21.9.
Our data extend this comparison about two orders of magnitude lower than
previously possible and provide the first image of the Lyman limit absorption
system associated with an L* galaxy. (abridged)
