The Speedtouch 330 is not a firewall / router - it's a plain old USB-RJ11 ADSL bridge.
Totally reliant on a software firewall for any protection.
If you want a hardware firewall, probably best to go for an integrated ADSL firewall / router - possibly with built-in wireless access also. This will completely replace your Speedtouch 330.
Lots of vendors - Linksys, Draytek, Netgear, Buffalo...
I can't recommend a specific model, as I have cable rather than ADSL, but Linksys and Draytek have a particularly good reputation, with Netgear perhaps a little bit behind.
SD