float4

we have a database (linux, 6.4.2, new odbc, connections from msaccess / 
win98) -- access doesn't fully appreciate the monetary type in postgres, so 
we made all monetary fields FLOAT4's.  weird stuff -- or maybe not to you 
-- we insert 23516.69 into a float4 field directly in psql, and then select 
it, and it shows 23516.7.  this is not good for a field used for MONEY!!! what are the limitations of float4?  should i
haveused float8?
 

thanks for any help you can offer. . .

jt