URL rewrite syntax unix

[joe2]

Hi,

i hv written
RewriteEngine on
RewriteRule ^{/a/([0-9]+)/([0-9]+).html} /myfile.php?x=$1&y=$2

it is working fine at win2k with apache 2.0.50.
But at webserver apache 1.3.31 (Unix)
it is throwing 404 error.
Is there anything wrong with the syntax.
Please advice.

Thanks in advance.