im looking to get a better audio system for my corsa, but have no idea where to start. ive been looking on ebay and have found some cheap items for it, are these good? or necessary?

two subwoofers:

1) http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=250711186956&ssPageNam e=STRK:MEWAX:IT

2) http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=200531659683&ssPageNam e=STRK:MEWAX:IT

Speakers: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=200531358012&ssPageNam e=STRK:MEWAX:IT - are these any good?

Amplifier - alpine mrv - f450: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=120633545595&ssPageNam e=STRK:MEWAX:IT


is there anything else need or anything better to get?

thanks