At the moment virtualization.info cannot confirm if any of the two deals is really in discussion, but both of them are realistic.
Cisco heavily invested in VMware just before its IPO, demostrating a strong interest in extending its dominance beyond the networking and security worlds.
A hypervisor would fit the dynamic datacenter strategy that Cisco is already pursuing with its VFrame, and would provide a new space where to place its networking devices (even if in virtual format).
IBM is deeply involved in virtualization technologies since ever, contributing to the Xen and KVM hypervisors code development.
Considering that Big Blue invented virtualization 40 years ago, the company must be uncomfortable in its current marginal role in this industry.
Additionally, IBM would be able to enrich XenServer with several critical components: the enterprise management solution (IBM Director, Tivoli), the high-availability solution (Systems Director Virtual Availability Management), the capacity planning solution (CDAT), the security solution (codename PHANTOM) and others.
During the last few years IBM certified its hardware for the Citrix hypervisor, and integrated its solutions with Xen for different projects (like a VDI platform or a general-purpose grid computing solution).
Acquiring Citrix, IBM would be able to offer (and certify) one of the most complete virtualization stack available on the market, pretty much like Sun is trying to do with the upcoming xVM Server.
(or maybe somebody just took seriously the idea that HP may buy Parallels)