Well, wireless is a great option if you have the right kit. I game online on Battlefield 2 over wireless with pings of around 15 to 25ms and downloads are at the speeds I would expect from my connection.
My setup is a Netgear WGT624 v3 Router and I can connect back to the router from ranges upto 300mtrs.
If I was you I'd try connecting wired to the router and see if the connection improves, if it does that that rules out the ISP and points to something within your wireless network, however if the connection doesn't improve this then points to the ISP (internet service provider).
Try the above suggestions and post back the results.
AMD Athlon 64 X2 Dual Core 4200+
DFI LanParty UT RDX200CF-DR Crossfire Motherboard
OCZ 4GB (4 x 1GB) PC3200 Dual Channel Platinum Series CAS2
ATI Radeon X1950Pro - Crossfire Edition - 512MB GDDR3 x2 cards installed.