okay, i'll bite... (41 chars--surely it can be done in less?)

map{exists$hash{$_}or$hash{$_}=999}@mips

update: (39 chars)

exists$hash{$_}or$hash{$_}=999for@mips
[download]

update2: vavoom is right. back to the drawing board... (75 chars--results in %h, and it's a little obfuscated)

@$_{@mips}=(999)x@mips for\my%h;exists$hash{$_}and$h{$_}=$hash{$_}for@
+mips;
[download]

~Particle