On 802.11g (standard 802.11g without frame bursting), even at great signal strength, no noise, always getting the 802.11g max 54 Megabit/sec PHY rate, no contention, and very efficient and well-tuned software, your maximum TCP/IP throughput is likely to be only around 23 Megabit/sec (about 2.7 MebiBytes/sec). If both machines are wireless, on the same AP, every packet would have to traverse the channel twice, cutting the bandwidth in half, for an effective throughput of about 1.4 MebiBytes/sec. If you were using a protocol that is not optimized for efficient file transfers, such as a remote filesystem protocol like SMB, that might cut your effective throughput significantly as well.
Overall, it's really easy to get down to a 256 KibiByte/sec throughput wireless-to-wireless SMB file copy speed over 802.11g under everyday, imperfect conditions. Those speeds may have seemed fine to users in 2003 when 802.11g was new, but they suck by 2013's 1300 Megabit/sec 3-stream 802.11ac standards.