Matt, from WHMCS, has just confirmed that he will, indeed, be working toward interfacing with the Interworx control panel. This means all of us JagPC Dedicated Server and VPS owners who use the Interworx CP will soon be able to install WHMCS. THREE CHEERS!!

Here are snippets from Matt's reply (I asked, and he gave me permission to relay this information)...
I have emailed Socheat at Interworx yesterday but haven't yet received a response. I can confirm I am looking into it for you and will do everything I can to get it implemented in the not too distant future - my request to Socheat was for some code samples or a testing environment so might just be taking him some time sort that out...
...we will be integrating with it provided we get co-operation from Interworx. Can't offer any ETA yet though.
So, thank you, Matt, for not abandoning us Interworx users!!
And, thank you in advance, Socheat for making it possible to interface with WHMCS.
And thank you, Greg, for being such an excellent, reliable and responsive host and allowing us VPS owners to choose Interworx.

So, finally INTERWORX the best dedicated server/hosting control panel system, will be able to join hands with WHMCS, the best client management/billing and support system...and we can do it all on JAGUARPC, the best internet hosting provider in the world!

Ahhh, life is good.... You guys are the best!!