  We present the first in a series of papers studying the X-ray properties of
28 early type galaxies spanning ~3 orders of magnitude in L_x. We report
emission-weighted constraints for Fe, O, Ne, Mg, Si, S and Ni. We find no
evidence of the very sub-solar Z_Fe historically reported, confirming a trend
in recent X-ray observations of bright galaxies and groups, nor do we find Z_Fe
correlates with L_x. In general we find no evidence for multi-phase ISM,
indicating multi-temperature fits found with ASCA were due to temperature
gradients Chandra can resolve. We compare the stellar Z_Fe, estimated from
simple stellar population model fits, to Z_Fe(ISM). Excepting one possible
outlier we find no evidence that the gas is much more metal-poor than the stars
and, in a few systems Z_Fe(ISM) is higher. In general the two exhibit similar
Z_Fe, which is inconsistent with both galactic wind models and recent
hierarchical chemical enrichment simulations. Adopting standard SNIa and SNII
metal yields our abundance ratio constraints imply 66+/-11% of the Fe within
the ISM was produced in SNIa, similar to the Solar neighbourhood and implying
similar enrichment histories for the ISM in a spiral and in elliptical
galaxies. Although these values are sensitive to systematic uncertainties in
the SN yields, they are in good agreement with observations of more massive
systems, indicating remarkable homology in the enrichment process operating
from cluster scales to low-to-intermediate L_x galaxies. The data also
uniformly exhibit the low Z_O/Z_Mg abundance ratios which have been reported in
some other systems. This is inconsistent with metal-production calculations in
SNII and may indicate an additional source of enrichment, such as Population
III hypernovae.(abridged)
