Copying "IF" formulas

Hi,
I've got some formulas in a job list file that lists all of the jobs our plumbing shop has done; they look like this:

=IF('C:\Documents and Settings\Compaq_Owner\my documents\excel\[21550.xls]Invoice'!$H$2=0,"-",'C:\Documents and Settings\Compaq_Owner\my documents\excel\[21550.xls]Invoice'!$H$2)

Everytime we create a new work order, we name the file the number of the work order (so like "21550" in this case). Right now, the IF formulas access the invoice information from the work order (there is a tab in the work order where we can invoice everything), including the amount, date, and invoice #. It takes this information and puts it into this job list file, and if there is nothing invoiced, it comes up with "-". In order to continue the formulas, right now I'm copying the formulas and manually changing the name of the file #. If I try to just copy and paste the formulas, the job file # stays the same, but I want it to change to the next number each time. Is there any way to do this quicker? Also, you should maybe know that in column A in this job list file, we currently have the job number/work order number listed, so I was trying to put in a cell# instead of the file #, like this:

=IF('C:\Documents and Settings\Compaq_Owner\my documents\excel\[[A100].xls]Invoice'!$H$2=0,"-",'C:\Documents and Settings\Compaq_Owner\my documents\excel\[[A100].xls]Invoice'!$H$2)

But this didn't seem to work. Any other suggestions?
Thanks

Hey great...I got it to work!
I only needed to add ".xls" after the cell number and fiddled around with inputting the function under "more function", and it worked.
Thanks!