"I have a old computer downstairs and i was wondering, is it possible to get 2 wireless cards, and use one to connect to my router for the internet and the other being an access point?"
I assume this is your attempt to “filter” all access to the wireless router through that machine, adding some software (???) that will manage bandwidth, filter content, etc.
Yes, you could do it (sort of). You could have the first wireless adapter connected to the wireless router, the second established as a wireless network, and use ICS to create a gateway between them. Of course, the second wireless connection will need to use a different wireless freq/channel. And realize the second wireless network is on its own subnet, has its own DHCP server, etc.
[modem]<--wire-->[wireless router]<--wireless-->[pc w/ (ics enabled)]<--wireless-->[pc, printer, xbox, …]
But it’s important to understand the limitations. Most wireless adapters can only be established as an adhoc network (not infrastructure), meaning you can only have a SINGLE wireless connection on that side of the gateway. However, if that computer supported Win7 (which seems highly unlikely), you could use something like Connectify and configure that wireless adapter in infrastructure mode (and then support multiple wireless clients).
http://www.connectify.me/
But even if the above was possible w/ Connectify, the configuration is unnecessarily complex. We can do better.
[modem]<--wire-->[pc (w/ ics enabled)]<--wire-->[wireless router]<<<--wire/wireless-->>>[pc, printer, xbox, …]
You could use a wireless connection between the modem and PC if necessary, although I would recommend against it since it just complicates the configuration. But you could theoretically use a WAP (wireless access point) at the modem and use it w/ the PC’s wireless adapter.
[modem]<--wire-->[wap]<--wireless-->[pc (w/ ics enabled)]<--wire-->[wireless router]<<<--wire/wireless-->>>[pc, printer, xbox, …]
Ugh, just a wee bit too busy for my taste, but it would work.
That said, it seems the wrong approach.
There are wireless routers that support QoS, parental controls, etc., that might be sufficient. I can’t say for sure because I don’t know the full scope of the problem. QoS implementations vary widely, and may not address every problem. But that’s clearly the easiest and most straightforward approach if it meets your needs.
Another possibility is using that spare box and something like Astaro:
http://www.astaro.com/
The free version is full-featured (as far as I know) and supports up to 50 local IPs (should be enough for home use). It basically does what you’re attempting to do, plus the software, which includes QoS, bandwidth control, parental controls, anti-malware, etc. A very nice product. Of course, that’s a rather complex piece of software for the average home (and usually overkill). And being Linux based, I’m not sure it would necessarily handle wireless all that well (wired sure, but wireless is always a roll of the dice w/ Linux). You might want to consider a different architecture.
[modem]<--wire-->[astaro]<--wire-->[wireless router]<<<--wire/wireless-->>>[pc, printer, xbox, …]
The Astaro acts as an inline filter that fronts your entire network.
Or you could use the Astaro as a replacement for your current router.
[modem]<--wire-->[astaro (as router)]<--wire-->[wireless router (ap only, no routing)]<<<--wire/wireless-->>>[pc, printer, xbox, …]
The only thing your old router is doing is providing a switch and WAP (wireless access point), no routing. IOW, the connection between the Astaro and old router is LAN-to-LAN.
There are other open source solutions for Linux as well (SonicWall, Untangle, etc.). And I’m sure other options in lieu of ICS under Windows (e.g., WinGate).
Of all the possible solutions, short of a better commercial wireless router, this last one seems the best. Just choose the gateway product you prefer. Basically you’re moving responsibility for your network services over to a potentially much more powerful solution than that offered by commercial routers for not much cost, esp. if you have a machine already available (putting the cost to run it aside).