I dont know if Tiscali is a ADSL2 service, in general most of the the very high speed connections are ADSL2 such as Be Unlimiteds 24mb connection, I would suggest calling your ISP for clarification on this.

The Intel (R) PRO/Wireless 2200BG most certainly is not wpa2 complient as far as I am aware although some software upgrade may have changed this, there are however connection issues associated with this hardware.

http://www.intel.com/support/wireles.../cs-022509.htm

The issue is basically random disconnection, and I have seen it behave in a manner where it disconnects and reconnects straight after, this causes a page time out which shows as '404 error web page unavailable' in the browser.
Intel claim to have resolved this issue with driver updates, although other people including myself are not so sure.

Having said that the card should work with a 'G' setting and WEP on the router however it will never take advantage of the performance offered by the router and as such I would change it to a card that does once It has been clarified that you have a ADSL2 connection