Conversion Errors

Hello,

I have the following query that runs against a view:

select cast((convert(varchar, HD.Value)) as float)
from HardwareData HD
where (HD.PropertyName = 'Total Space' and HD.CategoryName = 'Disk Drive(s)')

This query works with no errors. When I add a where clause as follows, it breaks:

select cast((convert(varchar, HD.Value)) as float)
from HardwareData HD
where (HD.PropertyName = 'Total Space' and HD.CategoryName = 'Disk Drive(s)')
and cast((convert(varchar,HD.Value)) as float) > 9999999

I get a "Msg 8114, Error converting data type varchar to float." message. Why would the statement in the WHERE clause fail to convert to float and not the statement that's in the select statement? It's as if the where clause conversion is done against all of the data, not just against the subset specified by the first part of the where clause where I try to narrow it down by total space. Any ideas?

THANKS