I’m going to have about 15 IP phones and 15 10/100 computers all plugged into my 10/100 network switch. Should I be worried, and put the phones on a separte switch from the computer net?
How flexible are your users and how saturated is your network?
If it is within your budget then you should segregate your network, but it is not absolutely necessary to do this on small networks. If your users will not throw a fits if call quality is degraded then you can probably get by on your current network setup. If your network does not see alot of traffic then you will only notice problems if there is a broadcast storm or virus outbreak.
To QOS or not to.
The recommended way to setup a network for VOIP is to use QOS and VLANs. Switches that support such things are not cheap and it may be more cost effective to segregate your network using separate networks. Separate network setups have caveats, it makes it harder for end users to move themselves and you will need at least 2 ports at each desk.
Go for some Cisco 3560s and 7940s if your budget will allow. They are not cheap but POE, QOS, and VLANs will make your job easier.
i would put them on the same cheap switches. (Unless people will be copying movies etc internally at the same time).