No not at all, your specs are remarkably similar to the PC in my office (my parent's PC), Dual Core 2.6ghz, 2GB ram, AT&T, and amazingly enough, they have lag issues as well, yet my lower spec PC doesn't, I'm on wireless and they're hard wired to the modem as well, it's a strange issue but one I can't help with.
At first I thought it was your low key specs but that is clearly not the case, the only suggestion I can offer is to use CCleaner to clear out temp files and all that other stuff the internet leaves behind
CCleaner - Download
When installing make sure to deselect the option to install the Yahoo toolbar