Best way to update a large DB ?

[jbv at souslelogo.com]

Hi list,

I have a mySQL DB with about 400000 entries, and I need to update
190000 of them in the following way :
update myDB set col1 = "blah blah", col2 = "blah blah" where id = 12345 
limit 1

I have a file with all the requests that weights almost 200 Mb.
I can't upload it via phpMyadmin, because it's too big and running all 
the requests
in one go will end up with a server timeout.

I was thinking of a cron job that would trigger every minute or so, and 
run a short
script that would read successive portions of 100 requests and feed them 
so mySQL.

Any better idea ?
Thanks in advance.
jbv