Ive tried searching but can't find anything :S

what size are the front speakers in the 1.4 fabia I?

I've just fitted one of these to 2006 Fabia VRS, I assume same as yours. Went straight on., no messing with adapters

http://cgi.ebay.co.uk/vw-golf-mk4-bora-passat-seat-skoda-door-speakers-/360280611144?cmd=ViewItem&pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item53e265d948#ht_500wt_896

Fun bit is removing door trim, reasonably good walk through in Haynes manual or search forums, sure

I've seen something on this. If (when !) you break door clips these do the business ;

http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=120586919005&ssPageName=ADME:B:EOIBSA:GB:1123#ht_1233wt_656

Final point, speakers attached with 5mm rivets, easy enough to drill out, watch backs don't drop into door.

To attach new speaker I bought a pop riveter (complete with a selection of rivets) from Homebase for about £13