No you can't load balance as there is too much disparity in speed. A reasonable goal would be the T1 as backup only.
Hope this helps, please rate post if it does!
Just to clarify a bit further for the experts...
FIOS is mostly a marketing name for Verizon's (US major telco provider) new high speed replacement to their standard DSL services. They are basically slowly building out and replacing their copper lines with with all Fiber lines and offering Telecommunications bundles with Phone/TV/Internet.
It is handed off to the customer as an ethernet connection and I am 99.999% sure that the bandwidth is shared similiar to Cable internet and not guaranteed. In other words it is not a dedicated pipe like an OC3, et al.
www.verizon.com/fios if my clarification doesn't help get his question answered.
For my input to the answer (Note I don't consider myself an 'expert'):
Outbound traffic should have no trouble being routed out both connections, however if you are looking to run any servers behind your connection, it most likely is not going to be possible to load balance. Being a non-dedicated line and a <$100 per month solution, Verizon is very unlikely to establish any type of peering with your T1 providers to route your public ip addresses to you through their pipe.
You may be able to achieve some type of load balancing using round robin DNS and using static NAT translations by having 2 public ips (1 from each provider) mapped to the same internal server.
As a side note, I'm also 99.999% sure that using a FIOS internet connection for the hosting of servers is a violation of their TOS and depending on what type of systems you are loooking to host behind it (if any) you may find some ports blocked upstream by Verizon (SMTP comes to mind).
Thanks caplinktech for the clarification.
One practical note, I've often see that when an ISP do such things like blocking ports and imposing restrictive AUPs (to still use the ancient name), you may find likely that people will vote with their feet and choose another carrier that doesn't.
(Is the FIOS hand-off Ethernet? I assume the FIOS is an Internet connection; the T1?)
If you're seeking proportional load balancing, especially in both directions, it could be very difficult to achieve.
For outbound, if your equipment supports it, and you're just using static defaults, OER/PfR might be your easiest solution.
Thanks for the responses everyone. Yeah, this is for Internet traffic for our company. We have both types of lines coming into this building and currently we are jamming all the Internet traffic out the T1, rather than using the FIOS line which is sitting hardly doing anything. I guess my best bet would be to switch the Internet traffic out to the FIOS line and use the T1 as a backup.
There may be an alternative for you to consider. You might set up your routing so that the FIOS is your primary outbound path with the T1 as a backup and then set up Policy Based Routing that will identify certain types of traffic (maybe its Email, maybe its web browsing, maybe its VPN, maybe its something else) and direct that particular traffic out the T1. This would allow you to use both link (at least to some extent) while maintaining the FIOS as the primary path and the T1 as the backup path.
Depending on your contract/costs/SLA/need for an SLA, if you are not hosting any services that would be in violation of TOS/AUP and are simply looking for outbound connectivity redundancy, you may also want to consider pulling the T1 altogether and replacing it with something like a business class cable internet connection for backup connectivity purposes. Again this idea, moreso hinges upon, the size of the company and the relative cost of the T1 solution compared to their budget more than anything else.
IE, probably a great idea for a company of <10-15 employees, not as good for a larger company as the cost outlay is negligible compared to other expenditures.