Try this.
Open a COPY of your workbook. Press Alt-F11 to open the VBA editor. From the menu, click Insert > Module. On the sheet that opens, paste this code:
Go back to your workbook. Somewhere on your sheet, select a cell, and enter the parameters like you said, for example:
<tbody>
[TD="align: center"]8[/TD]
[TD="align: right"]1200[/TD]
[TD="align: center"]9[/TD]
[TD="align: right"]100[/TD]
[TD="align: center"]10[/TD]
[TD="align: right"]5[/TD]
[TD="align: center"]11[/TD]
[TD="align: right"]75[/TD]
[TD="align: center"]12[/TD]
[TD="align: right"]4[/TD]
[TD="align: center"]13[/TD]
[TD="align: right"]25[/TD]
[TD="align: center"]14[/TD]
[TD="align: right"]8[/TD]
[TD="align: center"]15[/TD]
[TD="align: right"]150[/TD]
[TD="align: center"]16[/TD]
[TD="align: right"]1[/TD]
[TD="align: center"]17[/TD]
[TD="align: right"]50[/TD]
[TD="align: center"]18[/TD]
[TD="align: right"]1[/TD]
</tbody>
Initial amount, payment 1, # of times of payment 1, payment 2, # of times of payment 2, etc. You can make this list as long as you want, as long as it's in this format. If you have single payments, just put 1 for the number of times.
Now select the cell with the Initial amount, G8 in this example. Press Alt-F8, select PaymentMaker, and click Run. You should get this:
<tbody>
[TD="align: center"]8[/TD]
[TD="align: right"]1200[/TD]
[TD="align: center"]9[/TD]
[TD="align: right"]100[/TD]
[TD="align: center"]10[/TD]
[TD="align: right"]5[/TD]
[TD="align: center"]11[/TD]
[TD="align: right"]75[/TD]
[TD="align: center"]12[/TD]
[TD="align: right"]4[/TD]
[TD="align: center"]13[/TD]
[TD="align: right"]25[/TD]
[TD="align: center"]14[/TD]
[TD="align: right"]8[/TD]
[TD="align: center"]15[/TD]
[TD="align: right"]150[/TD]
[TD="align: center"]16[/TD]
[TD="align: right"]1[/TD]
[TD="align: center"]17[/TD]
[TD="align: right"]50[/TD]
[TD="align: center"]18[/TD]
[TD="align: right"]1[/TD]
[TD="align: center"]19[/TD]
[TD="align: right"][/TD]
[TD="align: center"]20[/TD]
[TD="align: right"][/TD]
[TD="align: center"]21[/TD]
[TD="align: right"][/TD]
[TD="align: center"]22[/TD]
[TD="align: right"]1200[/TD]
[TD="align: center"]23[/TD]
[TD="align: right"]1100[/TD]
[TD="align: center"]24[/TD]
[TD="align: right"]1000[/TD]
[TD="align: center"]25[/TD]
[TD="align: right"]900[/TD]
[TD="align: center"]26[/TD]
[TD="align: right"]800[/TD]
[TD="align: center"]27[/TD]
[TD="align: right"]700[/TD]
[TD="align: center"]28[/TD]
[TD="align: right"]625[/TD]
[TD="align: center"]29[/TD]
[TD="align: right"]550[/TD]
[TD="align: center"]30[/TD]
[TD="align: right"]475[/TD]
[TD="align: center"]31[/TD]
[TD="align: right"]400[/TD]
[TD="align: center"]32[/TD]
[TD="align: right"]375[/TD]
[TD="align: center"]33[/TD]
[TD="align: right"]350[/TD]
[TD="align: center"]34[/TD]
[TD="align: right"]325[/TD]
[TD="align: center"]35[/TD]
[TD="align: right"]300[/TD]
[TD="align: center"]36[/TD]
[TD="align: right"]275[/TD]
[TD="align: center"]37[/TD]
[TD="align: right"]250[/TD]
[TD="align: center"]38[/TD]
[TD="align: right"]225[/TD]
[TD="align: center"]39[/TD]
[TD="align: right"]200[/TD]
[TD="align: center"]40[/TD]
[TD="align: right"]50[/TD]
[TD="align: center"]41[/TD]
[TD="align: right"]0[/TD]
</tbody>
Also, press Alt-F8 again. Select PaymentMaker, but this time click the Options... button. Where it says Shortcut key, you can put a letter in the box after Ctrl+. If you put a in that box, and click OK, you can now run this macro by just clicking Ctrl+a, you don't need to go through the Alt-F8 menu anymore.
Let me know how this works.