Have new Canon 400D (XTi) with kit lens & 10 yr old 50MM 1.8, 28-105 1:3.5-4.5 USM zoom. Need 17-85 IS zoom?

Got a Canon 400D (Rebel XTi) with kit lens since I had 3 Canon slrs before I went digitial with Sony cams 6 years ago and have several lenses not being used plus a 380 EX flash with E-TTL. My lens are a 10-year-old prime 50MM 1:1.8 lens plus a 10-year-old 28-105 1:3.5-4.5 USM zoom lens that work with the 400D. I am using the camera for general purpose photography -- parties, landscapes, events (parades not sports), urban shots, Christmas decor ,etc. Do I still need to acquire a zoom or other type of Canon lens with IS such as the EF-S 17-85 4-5.6 IS USM or 28-135 3.5-5.6 IS USM? Are these old lens better than the kit lens? Is the 380EX flash good enough or do I still have to buy the 430 EX?

I have the 28-135 IS lens and love it. The kit lens is decent for wide angle shots. The 17-85 is infinitely better but costs $$$. The only wider lens is the 10-22mm, which is around $680.

My only suggestion is try out what you have for now and upgrade if have a need. The 380EX may suit your needs, then again, it may not. I have a 580 which for me is total overkill, since I rarely shoot indoors. Don't waste money and buy something that you may not need. You may be better off getting a telephoto lens instead of the 28-135.

You'll start to reallize what your limitations are and where you want to upgrade. It's a learning process. (From experience, I know that I need a macro lens.)

Good luck and enjoy it!

I think you will find that your old flash may not sync properly with the new camera I had to upgrade mine. Secondly I use the kit lens the most however I also have the 50mm you have and it works wonderful. I was not able to use my old tamron lenses as the focus was not on and when asking a dealer I found that to have those lenses redone to work with the digital it would cost as much as new lenses. If you can afford the IS go for it you won't regret it but it isn't absolutely necessary. Save for a great lens like the 70-200 2.8, you'll get far more use out of it esp shooting parades etc.

I'm not sure about the flash but your old lenses will work beautifully.
The 1.6 focal length multiplier really plays havoc on the usefulness of your old lenses though. On a 400D, your 50mm prime is effectively 80mm (nice for portraits, but not so great for general use anymore) and your 28-105mm zoom becomes 45-168mm.
The 18-55mm kit lens is one way to regain wide angle coverage, but the image quality is rather poor. The 17-85mm you mentioned is very nice, and perfect as a standard zoom with the Canon 400D/ 30D. It effectively provides 27-136mm on these cameras, putting you right back where you were with the 28-105mm zoom on a film body.
The 28-135mm that you also mentioned is awkward after the 1.6x conversion (as is the 28-105mm), so I wouldn't consider that.
I would hang on to the 50mm f/1.8 and sell the 2 zooms to finance a 17-85mm.