Hi sinfony, and welcome to the thinkbroadband forums.
You cannot have two DSL devices connected at the same time, so you will have to replace your USB modem with something else. Seeing as you want wireless, the obvious answer is to install a ADSL2+ 802.11n wireless router. This does three things - connects to your Internet provider using your DSL line, shares the connection over a handful of Ethernet ports and acts as a wireless base station.
ADSL2+ equipment supports all flavours of ADSL used in the UK, so if your connection is upgraded to use an 'up to 24Mbps' connection (now advertised as 'up to 16Mbps' to avoid incurring the wrath of the advertising standards people), your equipment will be ready. 802.11n is the latest ratified wireless standard.
If your computer has a wired Ethernet port, you just need a cable to connect the router and computer - you will probably get one with the router (and will need one to set the router up). If your computer lacks a wired Ethernet port, you will need to install an inexpensive network card inside it. The Device Manager in Windows may help if you are not sure - look under Network Adapters. A glance at the back of the computer may also help - you're looking for something similar to but wider than the socket used to connect your Voyager to the phone line, which will have 8 wires in the hole.
Your computers will see the Internet connection as via a network, so there's no user name and password to enter on each computer, though the wireless computer will need details of your wireless security setting entering. The AOL user name and password go into the router, along with a handful of other settings about your AOL connection (which you may be able to read out of the Voyager settings or find on the AOL web site, as they will be generic rather than account specific). I believe AOL will use PPPoA, so, alongside that, you will need to configure VPI (probably 0), VCI (probably 38), encapsulation (probably VC) and the user name and password you currently use with the Voyager. No UK ISP uses ATM quality of service - if the router asks you to set that, just choose UBR. The settings on an individual router may look slightly different to this - just choose the closest.
If you get the settings wrong, the router won't connect. You can configure the router initially with it connected to your computer via an Ethernet cable. When you think you have the settings correct, hook it up to your phone line in place of the Voyager modem. If the router doesn't connect to the Internet and you can't figure it out, simply disconnect the router and return to the Voyager modem temporarily.
I presume the Windows 7 computer has built in wireless - I'm assuming it is a laptop. If not, you will need wireless hardware for it - usually these come in the form of a USB stick.
I'm a little out of touch as to what is available in consumer routers - my home network is made up of business grade gear as our requirements are more demanding than most. I have bought networking gear from Broadband Buyer
, who are local to me - I have no connection other than as a satisfied customer. In addition to seeing what others recommend and reviewing Broadband Buyer's list of ADSL2+ 802.11n wireless routers
(biasing your search towards the cheaper end - your requirements are modest so there's no 'added value' from more expensive gear), I'd consider giving them a ring and seeing what they'd recommend - they're on a geographic phone number. If nothing else, Broadband Buyer will provide another data point.
For wireless security, make sure you disable WPS (sometimes called one-button setup) as it has security issues and use WPA2-Personal (may be called WPA2-PSK) with a 63 character long random password to prevent hackers from mounting a 'dictionary attack' (where they try combinations one at a time). It may be a pain to enter, but you only have to do it once per wireless device and you can always copy and paste it from a text file on a USB memory stick.
To start with, I'd concentrate on getting the wired computer working with a router - you can configure the wireless part of the router to 'disabled'. You can treat the wireless setup as a separate project.
I hope this is a helpful start. If you identify a router of interest you can go to the manufacturer's web site and download the manual. Hopefully, when put together with the information in this post, you can make sense of it.