You can use your old chainset and front mech with 9 speed Ergos no problem. I've done it in the past. Your rear mech will not work optimally unless it is a Campag 9/10 speed. 8 speed mechs kind of work but not 100% in my experience.
The minimum you need is 9 speed Ergo shifters, a 9/10 speed rear mech to go with your 9 speed wheel, a nice wide cassette (but 28t is the max on 9 speed I think), a 9 speed chain and crucially a way of attaching the downtube cable stops onto your frame. You don't have braze-ons for downtube shifters but if you're lucky the cable stops will fit on the band your existing shifters are using.
You could use indexed downtube shifters instead of Ergos - I have these and really like them. 8 speed Veloce ones turn up on eBay quite regularly and can be "upgraded" to 9 or 10 speed with the relevant spare part. I'm about to try and get said spare part to go 10 speed on one of my sets so I'll find out if that's truth or Internet fiction. Again you'll need a suitable band to mount these on. The part number to get for the complete 8 speed Veloce downtube shifters is SL-11SVLCG. The earlier version can't be upgraded.
When you're looking for rear mechs get the 2nd generation which have 9 speed written on them and the cage adjusting screw on the lower pivot not the top pivot. That would be 2001 onwards. These work on 9 or 10 speed. I've just noticed that Campag say the 9 speed downtube levers only work with the earlier 9 speed rear mechs.
If you get a 2nd gen rear mech you need to get the right Ergos as well. They also have 9 speed written on them.
A bit complicated I know but stick with it!