Would it be a problem if somebody subscribe for an 1Gb internet connection, but have 10/100Mbps LAN Chip in one of its computer? I have wondered as the provider's site shows 1Gb Card as a minimum requirements, i5/i7 processor, 4GB RAM, which are not an option on the computer. Is it a problem which will not enable the computer to connect to the internet, or it will be "only" slower?
That wont be an issue the only downside is you wont be able to make use of its full potential.
It will be "only" slower, if you want to put it that way.
However, what doesn't make sense here is buying a gigabit connection only to use it with a slow network card. Even then, sure, the computer will be able to connect to the network and browse at 100mbps, since the protocols are backward compatible.
However, as Ron Maupin has pointed out, it is possible that the equipment may not support slow speeds, but it is unlikely for consumer equipment.