Advice on merging disparate ERP systems

I may soon be in an new IT management position where I will be responsible for taking a SME manufacturing company forward in regards to updating existing systems / implementing usuage policies / staff training / infrastructure management / comms etc. They have recently acquired another similar business (hence the openning) and have therefore two incompatiblle ERP systems amongst other issues.

Can anyone offer some useful advice as to the best approach to take this company forward and what pitfalls to look out for, in addition to any warning signs to recognise.

PS. This company will probably need an overhaul of their e-mail, network infrastructure, Internet access and communication between two geographically located sites.