PC Expert. I was trying to avoid having to key all of this which is the reason for the terseness of my original answer. Please take this kindly but you may be a PC Expert but I am a networking expert.
The reason that I said a Wireless Hub won't work is, for start, there is no such thing as a Wireless Hub. (In order to implement a WiFi network one needs a Wireless Access Point, even if it is built-in to another device like a router.) Hubs are dumb devices that connnect wired Ethernet devices to each other. They are also old technology as Ethernet Switches have largely replaced them. However neither Switches not Hubs are clever enough to serve IP addresses nor route between networks. In order share an Internet connection one needs a router. (BT have muddied the water by calling their routers Home Hubs but that is purely market phrase.)
So the OP would need a router that can route between a dial-up WAN Connection and his/her LAN and I have never come across such a thing. The domestic routers on the market route between an ADSL WAN connection and a LAN or an Ethernet Cable connection and a LAN.
In your scenario something must be serving IP Addresses to the devices (or you are setting them up manually) or they wouldn't be able to talk to each other. Nor would such setup be able to route between networks.
I suspect that you may have a router with built-in Ethernet switch and a built-in Wireless Access Point.
Funny that as I have a wireless hub and one of the 4 PC's connected to thes HUB has a printer attached and if I share the printer all the other PCs which talk to the wireless hub can use the printer. The PC with the printer connected has to be switch on of course.
So the same can be true for a dial up connection once the internet connection has been shared.
I am afraid that that answer about using a wireless hub won't actually work for several reasons.
However you can use your existing PC to connect another one to the Internet wirelessly by using Internet Connection Sharing. (Its described on www.microsoft.com) However on dial-up it really isn't worth the bother. I suggest that you just connect the PCs to the dial-up connection as and when needed - or get Broadband.
You would need a wireless hub and then set the PC connected to the phone line to allow other users the see the internet connection.
However, dial up is really slow so adding another PC it will be even slower. Better to get yourself broadband and many companies like Orange can supply this free if you have a mobile phone contract. Most (if not all) broadband supplies will give you a free wireless router