2001 should be EODB compatible ... you can pick up a handheld code scanner from fleabay for about £15 on fleabay ... unidiag software is free, but you'll have to buy a KKL interface for £12 (ish) on fleabay ... alfadiag is about £50 and you'll need the same KKL interface ...
(unidiag has more functionality than alfadiag, but is more difficult to set up)
alternatively if you want something that just works out of the box then engine check from gendan is pretty good ... although you'll be looking at about £100 ...
(SEARS on here seems to know most about diagnostics, especially unidiag, if you check out his signature he's got a link to a unidiag how to ...)
Alfa 156 10v 2.4 JTD + AHM fitted Koni FSDs, Eibach Pro Kit Springs,
AHM 200+BHP remap, Q2, 8C Alloys, GTA lights, Leather Interior...
CarPuter Spec: Gigabyte MA785GM Motherboard,2Gb Ram,
AMD Athlon X2 5050e Socket AM2 45W CPU,
K8061 D/A converter, M4 ATX PS, 60Gb SSD, Garmin x20 GPS