Huge Performance Loss When Using Variables

was trying to performance tune a query and came up on this weird issue(Weird to me atleast.. possibly because I am a newbie:-))).

When I run the query mentioned below, I get the results in 1 second, while the same query, if I declare a variable for the value I am comparing, it takes 40 seconds. I am on SQL Server 2000. Both queries are being run in the same DB on the same tables and the only difference between the two is that the date has been declared as a variable. I am able to consistantly reproduce this. Tried casting the variable, declaring it as varchar , replacing the date by getdate() at both places, but the moment I use the variable, the performance goes for a toss. Has anyone came across any similar issues?
TIA
Callista

Query 1
select ae.Col1, ae.Col2, ae.Col3, ae.Col4, ge.Col4, c.Col5, 0
from table1 ae WITH (INDEX=ind_Col3 NOLOCK), table2 ge with (nolock), table3 c with (nolock)
where ae.Col1 = ge.Col1
AND ae.Col4 = c.Col1
AND ae.Col3 > '2007-10-25 14:18:12.380'
and ae.Col6 is not null

Query 2
declare @MyVariable datetimeselect @MyVariable = '2007-10-25 14:18:12.380'
select ae.Col1, ae.Col2, ae.Col3, ae.Col4, ge.Col4, c.Col5, 0
from table1 ae WITH (INDEX=ind_Col3 NOLOCK), table2 ge with (nolock), table3 c with (nolock)
where ae.Col1 = ge.Col1
AND ae.Col4 = c.Col1
AND ae.Col3 > @MyVariable
and ae.Col6 is not null