Download rename as rename.pl. On the command line, type:
perl rename.pl -n "s{(\d+)(?= - \d+\.jpg$)}{ sprintf q(%03d), $1 }e" *
+.jpg

[download]

Remove -n switch to actually do the renaming.

Note: Command provided is quoted for cmd.exe.

Update: Added more details.

In reply to Re: Mass file renaming help by repellent
in thread Mass file renaming help by Bastille

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