UBB.Threads 7.x is the replacement for both UBB.Classic and UBB.Threads, which are both now EOL. UBB.Threads7 is basically a complete rewrite of all basecode.
As a strong advocate of UBB.Classic, even I love UBB.Threads and woudln't even think of going back, and I was with classic since as long as i can remember...
You can import your old data to threads, so it's not really starting from scratch
... And if you don't feel comfortable about doing the upgrade/import yourself, you could always hire someone (ahem, me, ahem) to do it for you.