For Q2 2006 over Q2 2005, IBM, HP and Dell all lost market share - and Sun gained. For Q2 over Q1 this year, IBM and Sun gained but HP and Dell lost. There's certainly a fair amount of seasonality here. I decided to make a little table from IDC results:

Worldwide Server Systems Factory Revenue
      Q105   Q205   Q305   Q405   Q106   Q206
IBM:  28.3%  31.9%  32.3%  38.4%  27.9%  31.0%
HP:   27.6%  28.5%  27.8%  26.8%  28.1%  27.8%
Dell: 10.8%  10.5%  10.5%  9.6%   11.1%  10.3%
Sun:   9.9%  11.3%   8.7%  8.2%   10.8%  12.9%

Q2 is seasonally Sun's strongest quarter, but up from 11.3% to 12.9% on a year ago is nice.

For actual revenue (year on year): IBM was down 2.2%, HP was down 1.7%, Dell was down 1.3%, and Sun was up 15.5%.



For reference, here's the relevant press releases (oldest to newest):
http://www.idc.com/getdoc.jsp?containerId=prUS00153905
http://www.idc.com/getdoc.jsp?containerId=prUS00223005
http://www.idc.com/getdoc.jsp?containerId=prUS20013705
http://www.idc.com/getdoc.jsp?containerId=prUS20074406
http://www.idc.com/getdoc.jsp?containerId=prUS20180706
http://www.idc.com/getdoc.jsp?containerId=prUS20323506